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  1. title: i18n with tagged template strings in ECMAScript 6
  2. url: http://jaysoo.ca/2014/03/20/i18n-with-es6-template-strings/
  3. hash_url: 68f2d862066c644a50f929e8a787406b
  4. <p>One of the new features coming to ECMAScript 6 (ES6), the next version of
  5. JavaScript standards, is the <strong>template string</strong>. The simplest use cases for
  6. template strings are creating multiline strings, and doing string interpolation.</p>
  7. <p>Multiline string:</p>
  8. <div class="highlight"><pre><code class="javascript"><span class="kd">let</span> <span class="nx">s</span> <span class="o">=</span> <span class="err">`</span><span class="nx">This</span> <span class="nx">is</span>
  9. <span class="nx">a</span> <span class="nx">multiline</span>
  10. <span class="nx">string</span><span class="err">`</span><span class="p">;</span>
  11. </code></pre></div>
  12. <p>String interpolation:</p>
  13. <div class="highlight"><pre><code class="javascript"><span class="kd">let</span> <span class="nx">firstName</span> <span class="o">=</span> <span class="s1">'Bob'</span><span class="p">,</span> <span class="nx">lastName</span> <span class="o">=</span> <span class="s1">'Smith'</span><span class="p">;</span>
  14. <span class="kd">let</span> <span class="nx">msg</span> <span class="o">=</span> <span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">firstName</span><span class="p">}</span> <span class="nx">$</span><span class="p">{</span><span class="nx">lastName</span><span class="p">}</span><span class="o">!</span><span class="err">`</span><span class="p">;</span> <span class="c1">// 'Hello Bob Smith!'</span>
  15. </code></pre></div>
  16. <p>You can also <strong>tag</strong> a template string by adding an expression before it.
  17. When a template string is tagged, the literals and substitutions are passed to
  18. the tag function, and whatever returns from the function is the resulting value.</p>
  19. <div class="highlight"><pre><code class="javascript"><span class="kd">function</span> <span class="nx">foo</span><span class="p">(</span><span class="nx">literals</span><span class="p">,</span> <span class="p">...</span><span class="nx">values</span><span class="p">)</span> <span class="p">{</span>
  20. <span class="k">return</span> <span class="mi">42</span><span class="p">;</span>
  21. <span class="p">}</span>
  22. <span class="nx">foo</span><span class="err">`</span><span class="nx">What</span> <span class="k">do</span> <span class="nx">you</span> <span class="nx">get</span> <span class="k">if</span> <span class="nx">you</span> <span class="nx">multiply</span> <span class="nx">$</span><span class="p">{</span><span class="mi">6</span><span class="p">}</span> <span class="nx">by</span> <span class="nx">$</span><span class="p">{</span><span class="mi">9</span><span class="p">}</span><span class="o">?</span><span class="err">`</span><span class="p">;</span> <span class="c1">// 42</span>
  23. <span class="c1">// In the foo function:</span>
  24. <span class="c1">// literals = ['What do you get if you multiply ', ' by ', '?']</span>
  25. <span class="c1">// values[0] = 6</span>
  26. <span class="c1">// values[1] = 9</span>
  27. </code></pre></div>
  28. <p>This feature opens up some interesting syntactic sugar for producing and manipulating
  29. content. One such example is <strong>Internationalization</strong> or <strong>i18n</strong>.</p>
  30. <p>In this post we’ll look at:</p>
  31. <ul>
  32. <li>Implementing a basic i18n tag function for translating messages.</li>
  33. <li>Localization (l10n) of values using the <strong>Intl</strong> native object.</li>
  34. </ul>
  35. <p>This post requires some knowledge of new ES6 features such as array comprehensions,
  36. arrow functions, spreads, etc. If you are new to ES6, I suggest brushing up on the
  37. basics. I found Ariya’s <a href="http://ariya.ofilabs.com/tag/es6">posts on ES6</a> to be useful.</p>
  38. <h2 id="the-i18n-tag">The i18n tag</h2>
  39. <p>Let’s start with an example of how we want to use the <code>i18n</code> tag.</p>
  40. <div class="highlight"><pre><code class="javascript"><span class="kd">let</span> <span class="nx">name</span> <span class="o">=</span> <span class="s1">'Bob'</span><span class="p">;</span>
  41. <span class="kd">let</span> <span class="nx">amount</span> <span class="o">=</span> <span class="mi">100</span><span class="p">;</span>
  42. <span class="nx">i18n</span><span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span><span class="p">(</span><span class="nx">CAD</span><span class="p">)</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span>
  43. </code></pre></div>
  44. <p>Here, we are expecting to translate the literals into the language of our choosing.
  45. We are also adding optional annotations to the substitutions. In this case, the
  46. <code>amount</code> value has the <code>:c(CAD)</code> annotation, which marks it as a currency <strong>type</strong>
  47. that is in Canadian Dollars (CAD).</p>
  48. <p>If we translated this string to German, for example, we expect the result to be
  49. <code>'Hallo Bob, Sie haben 1.234,56 $CA auf Ihrem Bankkonto.'</code> Note that the currency
  50. amount has thousands and decimal separator as per German locale.</p>
  51. <h2 id="implementation">Implementation</h2>
  52. <p>We’ll allow configuration of our <code>i18n</code> tag through <code>I18n.use</code>.</p>
  53. <div class="highlight"><pre><code class="javascript"><span class="kd">let</span> <span class="nx">messageBundle_de</span> <span class="o">=</span> <span class="p">{</span>
  54. <span class="s1">'Hello {0}, you have {1} in your bank account.'</span><span class="o">:</span> <span class="s1">'Hallo {0}, Sie haben {1} auf Ihrem Bankkonto.'</span>
  55. <span class="p">};</span>
  56. <span class="kd">let</span> <span class="nx">i18n</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">use</span><span class="p">({</span>
  57. <span class="nx">locale</span><span class="o">:</span> <span class="s1">'de-DE'</span><span class="p">,</span>
  58. <span class="nx">defaultCurrency</span><span class="o">:</span> <span class="s1">'EUR'</span><span class="p">,</span>
  59. <span class="nx">messageBundle</span><span class="o">:</span> <span class="nx">messageBundle_de</span><span class="p">});</span>
  60. <span class="c1">// Now we can translate our string to German, with the Euro being the default currency</span>
  61. <span class="nx">i18n</span><span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span><span class="p">(</span><span class="nx">CAD</span><span class="p">)</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span>
  62. <span class="c1">// =&gt; Hallo Bob, Sie haben 1.234,56 $CA auf Ihrem Bankkonto.</span>
  63. </code></pre></div>
  64. <p>Let’s start with implementing the <code>I18n.use</code> method, which should return the
  65. tag function.</p>
  66. <div class="highlight"><pre><code class="javascript"><span class="kd">let</span> <span class="nx">I18n</span> <span class="o">=</span> <span class="p">{</span>
  67. <span class="nx">use</span><span class="p">({</span><span class="nx">lang</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="p">})</span> <span class="p">{</span>
  68. <span class="nx">I18n</span><span class="p">.</span><span class="nx">lang</span> <span class="o">=</span> <span class="nx">lang</span><span class="p">;</span>
  69. <span class="nx">I18n</span><span class="p">.</span><span class="nx">defaultCurrency</span> <span class="o">=</span> <span class="nx">defaultCurrency</span><span class="p">;</span>
  70. <span class="nx">I18n</span><span class="p">.</span><span class="nx">messageBundle</span> <span class="o">=</span> <span class="nx">messageBundle</span><span class="p">;</span>
  71. <span class="k">return</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">translate</span><span class="p">;</span>
  72. <span class="p">},</span>
  73. <span class="nx">translate</span><span class="p">(</span><span class="nx">literals</span><span class="p">,</span> <span class="p">...</span><span class="nx">values</span><span class="p">)</span> <span class="p">{</span>
  74. <span class="kd">let</span> <span class="nx">translationKey</span> <span class="o">=</span> <span class="p">...;</span>
  75. <span class="kd">let</span> <span class="nx">translationString</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">messages</span><span class="p">[</span><span class="nx">translationKey</span><span class="p">];</span>
  76. <span class="k">if</span> <span class="p">(</span><span class="nx">translationString</span><span class="p">)</span> <span class="p">{</span>
  77. <span class="kd">let</span> <span class="nx">localizedValues</span> <span class="o">=</span> <span class="p">...;</span>
  78. <span class="k">return</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">_buildMessage</span><span class="p">(</span><span class="nx">translationString</span><span class="p">,</span> <span class="p">...</span><span class="nx">localizedValues</span><span class="p">);</span>
  79. <span class="p">}</span>
  80. <span class="k">return</span> <span class="s1">'Error: translation missing!'</span><span class="p">;</span>
  81. <span class="p">}</span>
  82. <span class="p">};</span>
  83. </code></pre></div>
  84. <p>The <code>translationString</code> should match the keys in our message bundle. In our previous
  85. German translation example, this would be <code>'Hello {0}, you have {1} in your bank account.'</code>.</p>
  86. <p>The <code>localizedValues</code> array is a map of substitution <code>values</code> in their localized
  87. forms. For example, in German <code>1000.12</code> should show as <code>'1.000,12'</code>.</p>
  88. <p>Now, I will show a full implementation of the library.</p>
  89. <div class="highlight"><pre><code class="javascript"><span class="c1">// Matches optional type annotations in i18n strings.</span>
  90. <span class="c1">// e.g. i18n`This is a number ${x}:n(2)` formats x as number</span>
  91. <span class="c1">// with two fractional digits.</span>
  92. <span class="kr">const</span> <span class="nx">typeInfoRegex</span> <span class="o">=</span> <span class="sr">/^:([a-z])(\((.+)\))?/</span><span class="p">;</span>
  93. <span class="kd">let</span> <span class="nx">I18n</span> <span class="o">=</span> <span class="p">{</span>
  94. <span class="nx">use</span><span class="p">({</span><span class="nx">locale</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="p">})</span> <span class="p">{</span>
  95. <span class="nx">I18n</span><span class="p">.</span><span class="nx">locale</span> <span class="o">=</span> <span class="nx">locale</span><span class="p">;</span>
  96. <span class="nx">I18n</span><span class="p">.</span><span class="nx">defaultCurrency</span> <span class="o">=</span> <span class="nx">defaultCurrency</span><span class="p">;</span>
  97. <span class="nx">I18n</span><span class="p">.</span><span class="nx">messageBundle</span> <span class="o">=</span> <span class="nx">messageBundle</span><span class="p">;</span>
  98. <span class="k">return</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">translate</span><span class="p">;</span>
  99. <span class="p">},</span>
  100. <span class="nx">translate</span><span class="p">(</span><span class="nx">literals</span><span class="p">,</span> <span class="p">...</span><span class="nx">values</span><span class="p">)</span> <span class="p">{</span>
  101. <span class="kd">let</span> <span class="nx">translationKey</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">_buildKey</span><span class="p">(</span><span class="nx">literals</span><span class="p">);</span>
  102. <span class="kd">let</span> <span class="nx">translationString</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">messageBundle</span><span class="p">[</span><span class="nx">translationKey</span><span class="p">];</span>
  103. <span class="k">if</span> <span class="p">(</span><span class="nx">translationString</span><span class="p">)</span> <span class="p">{</span>
  104. <span class="kd">let</span> <span class="nx">typeInfoForValues</span> <span class="o">=</span> <span class="nx">literals</span><span class="p">.</span><span class="nx">slice</span><span class="p">(</span><span class="mi">1</span><span class="p">).</span><span class="nx">map</span><span class="p">(</span><span class="nx">I18n</span><span class="p">.</span><span class="nx">_extractTypeInfo</span><span class="p">);</span>
  105. <span class="kd">let</span> <span class="nx">localizedValues</span> <span class="o">=</span> <span class="nx">values</span><span class="p">.</span><span class="nx">map</span><span class="p">((</span><span class="nx">v</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span> <span class="o">=&gt;</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">_localize</span><span class="p">(</span><span class="nx">v</span><span class="p">,</span> <span class="nx">typeInfoForValues</span><span class="p">[</span><span class="nx">i</span><span class="p">]));</span>
  106. <span class="k">return</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">_buildMessage</span><span class="p">(</span><span class="nx">translationString</span><span class="p">,</span> <span class="p">...</span><span class="nx">localizedValues</span><span class="p">);</span>
  107. <span class="p">}</span>
  108. <span class="k">return</span> <span class="s1">'Error: translation missing!'</span><span class="p">;</span>
  109. <span class="p">},</span>
  110. <span class="nx">_localizers</span><span class="o">:</span> <span class="p">{</span>
  111. <span class="nx">s</span> <span class="cm">/*string*/</span><span class="o">:</span> <span class="nx">v</span> <span class="o">=&gt;</span> <span class="nx">v</span><span class="p">.</span><span class="nx">toLocaleString</span><span class="p">(</span><span class="nx">I18n</span><span class="p">.</span><span class="nx">locale</span><span class="p">),</span>
  112. <span class="nx">c</span> <span class="cm">/*currency*/</span><span class="o">:</span> <span class="p">(</span><span class="nx">v</span><span class="p">,</span> <span class="nx">currency</span><span class="p">)</span> <span class="o">=&gt;</span> <span class="p">(</span>
  113. <span class="nx">v</span><span class="p">.</span><span class="nx">toLocaleString</span><span class="p">(</span><span class="nx">I18n</span><span class="p">.</span><span class="nx">locale</span><span class="p">,</span> <span class="p">{</span>
  114. <span class="nx">style</span><span class="o">:</span> <span class="s1">'currency'</span><span class="p">,</span>
  115. <span class="nx">currency</span><span class="o">:</span> <span class="nx">currency</span> <span class="o">||</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">defaultCurrency</span>
  116. <span class="p">})</span>
  117. <span class="p">),</span>
  118. <span class="nx">n</span> <span class="cm">/*number*/</span><span class="o">:</span> <span class="p">(</span><span class="nx">v</span><span class="p">,</span> <span class="nx">fractionalDigits</span><span class="p">)</span> <span class="o">=&gt;</span> <span class="p">(</span>
  119. <span class="nx">v</span><span class="p">.</span><span class="nx">toLocaleString</span><span class="p">(</span><span class="nx">I18n</span><span class="p">.</span><span class="nx">locale</span><span class="p">,</span> <span class="p">{</span>
  120. <span class="nx">minimumFractionDigits</span><span class="o">:</span> <span class="nx">fractionalDigits</span><span class="p">,</span>
  121. <span class="nx">maximumFractionDigits</span><span class="o">:</span> <span class="nx">fractionalDigits</span>
  122. <span class="p">})</span>
  123. <span class="p">)</span>
  124. <span class="p">},</span>
  125. <span class="nx">_extractTypeInfo</span><span class="p">(</span><span class="nx">literal</span><span class="p">)</span> <span class="p">{</span>
  126. <span class="kd">let</span> <span class="nx">match</span> <span class="o">=</span> <span class="nx">typeInfoRegex</span><span class="p">.</span><span class="nx">exec</span><span class="p">(</span><span class="nx">literal</span><span class="p">);</span>
  127. <span class="k">if</span> <span class="p">(</span><span class="nx">match</span><span class="p">)</span> <span class="p">{</span>
  128. <span class="k">return</span> <span class="p">{</span><span class="nx">type</span><span class="o">:</span> <span class="nx">match</span><span class="p">[</span><span class="mi">1</span><span class="p">],</span> <span class="nx">options</span><span class="o">:</span> <span class="nx">match</span><span class="p">[</span><span class="mi">3</span><span class="p">]};</span>
  129. <span class="p">}</span> <span class="k">else</span> <span class="p">{</span>
  130. <span class="k">return</span> <span class="p">{</span><span class="nx">type</span><span class="o">:</span> <span class="s1">'s'</span><span class="p">,</span> <span class="nx">options</span><span class="o">:</span> <span class="s1">''</span><span class="p">};</span>
  131. <span class="p">}</span>
  132. <span class="p">},</span>
  133. <span class="nx">_localize</span><span class="p">(</span><span class="nx">value</span><span class="p">,</span> <span class="p">{</span><span class="nx">type</span><span class="p">,</span> <span class="nx">options</span><span class="p">})</span> <span class="p">{</span>
  134. <span class="k">return</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">_localizers</span><span class="p">[</span><span class="nx">type</span><span class="p">](</span><span class="nx">value</span><span class="p">,</span> <span class="nx">options</span><span class="p">);</span>
  135. <span class="p">},</span>
  136. <span class="c1">// e.g. I18n._buildKey(['', ' has ', ':c in the']) == '{0} has {1} in the bank'</span>
  137. <span class="nx">_buildKey</span><span class="p">(</span><span class="nx">literals</span><span class="p">)</span> <span class="p">{</span>
  138. <span class="kd">let</span> <span class="nx">stripType</span> <span class="o">=</span> <span class="nx">s</span> <span class="o">=&gt;</span> <span class="nx">s</span><span class="p">.</span><span class="nx">replace</span><span class="p">(</span><span class="nx">typeInfoRegex</span><span class="p">,</span> <span class="s1">''</span><span class="p">);</span>
  139. <span class="kd">let</span> <span class="nx">lastPartialKey</span> <span class="o">=</span> <span class="nx">stripType</span><span class="p">(</span><span class="nx">literals</span><span class="p">[</span><span class="nx">literals</span><span class="p">.</span><span class="nx">length</span> <span class="o">-</span> <span class="mi">1</span><span class="p">]);</span>
  140. <span class="kd">let</span> <span class="nx">prependPartialKey</span> <span class="o">=</span> <span class="p">(</span><span class="nx">memo</span><span class="p">,</span> <span class="nx">curr</span><span class="p">,</span> <span class="nx">i</span><span class="p">)</span> <span class="o">=&gt;</span> <span class="err">`</span><span class="nx">$</span><span class="p">{</span><span class="nx">stripType</span><span class="p">(</span><span class="nx">curr</span><span class="p">)}{</span><span class="nx">$</span><span class="p">{</span><span class="nx">i</span><span class="p">}}</span><span class="nx">$</span><span class="p">{</span><span class="nx">memo</span><span class="p">}</span><span class="err">`</span><span class="p">;</span>
  141. <span class="k">return</span> <span class="nx">literals</span><span class="p">.</span><span class="nx">slice</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">).</span><span class="nx">reduceRight</span><span class="p">(</span><span class="nx">prependPartialKey</span><span class="p">,</span> <span class="nx">lastPartialKey</span><span class="p">);</span>
  142. <span class="p">},</span>
  143. <span class="c1">// e.g. I18n._formatStrings('{0} {1}!', 'hello', 'world') == 'hello world!'</span>
  144. <span class="nx">_buildMessage</span><span class="p">(</span><span class="nx">str</span><span class="p">,</span> <span class="p">...</span><span class="nx">values</span><span class="p">)</span> <span class="p">{</span>
  145. <span class="k">return</span> <span class="nx">str</span><span class="p">.</span><span class="nx">replace</span><span class="p">(</span><span class="sr">/{(\d)}/g</span><span class="p">,</span> <span class="p">(</span><span class="nx">_</span><span class="p">,</span> <span class="nx">index</span><span class="p">)</span> <span class="o">=&gt;</span> <span class="nx">values</span><span class="p">[</span><span class="nb">Number</span><span class="p">(</span><span class="nx">index</span><span class="p">)]);</span>
  146. <span class="p">}</span>
  147. <span class="p">};</span>
  148. <span class="c1">// Usage</span>
  149. <span class="kd">let</span> <span class="nx">messageBundle_fr</span> <span class="o">=</span> <span class="p">{</span>
  150. <span class="s1">'Hello {0}, you have {1} in your bank account.'</span><span class="o">:</span> <span class="s1">'Bonjour {0}, vous avez {1} dans votre compte bancaire.'</span>
  151. <span class="p">};</span>
  152. <span class="kd">let</span> <span class="nx">messageBundle_de</span> <span class="o">=</span> <span class="p">{</span>
  153. <span class="s1">'Hello {0}, you have {1} in your bank account.'</span><span class="o">:</span> <span class="s1">'Hallo {0}, Sie haben {1} auf Ihrem Bankkonto.'</span>
  154. <span class="p">};</span>
  155. <span class="kd">let</span> <span class="nx">messageBundle_zh_Hant</span> <span class="o">=</span> <span class="p">{</span>
  156. <span class="s1">'Hello {0}, you have {1} in your bank account.'</span><span class="o">:</span> <span class="s1">'你好{0},你有{1}在您的銀行帳戶。'</span>
  157. <span class="p">};</span>
  158. <span class="kd">let</span> <span class="nx">name</span> <span class="o">=</span> <span class="s1">'Bob'</span><span class="p">;</span>
  159. <span class="kd">let</span> <span class="nx">amount</span> <span class="o">=</span> <span class="mf">1234.56</span><span class="p">;</span>
  160. <span class="kd">let</span> <span class="nx">i18n</span><span class="p">;</span>
  161. <span class="nx">i18n</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">use</span><span class="p">({</span><span class="nx">locale</span><span class="o">:</span> <span class="s1">'fr-CA'</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="o">:</span> <span class="s1">'CAD'</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="o">:</span> <span class="nx">messageBundle_fr</span><span class="p">});</span>
  162. <span class="nx">console</span><span class="p">.</span><span class="nx">log</span><span class="p">(</span><span class="nx">i18n</span> <span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span><span class="p">);</span>
  163. <span class="nx">i18n</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">use</span><span class="p">({</span><span class="nx">locale</span><span class="o">:</span> <span class="s1">'de-DE'</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="o">:</span> <span class="s1">'EUR'</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="o">:</span> <span class="nx">messageBundle_de</span><span class="p">});</span>
  164. <span class="nx">console</span><span class="p">.</span><span class="nx">log</span><span class="p">(</span><span class="nx">i18n</span> <span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span><span class="p">);</span>
  165. <span class="nx">i18n</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">use</span><span class="p">({</span><span class="nx">locale</span><span class="o">:</span> <span class="s1">'zh-Hant-CN'</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="o">:</span> <span class="s1">'CNY'</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="o">:</span> <span class="nx">messageBundle_zh_Hant</span><span class="p">});</span>
  166. <span class="nx">console</span><span class="p">.</span><span class="nx">log</span><span class="p">(</span><span class="nx">i18n</span> <span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span><span class="p">);</span>
  167. </code></pre></div>
  168. <p>One important thing to note here is that the <code>_localizers</code> are using the
  169. native <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl">Intl</a>
  170. object to localize values.</p>
  171. <h3 id="es-internationalization-api">ES Internationalization API</h3>
  172. <p>The <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl">Internationalization API</a>
  173. adds new methods to native types, such as <code>Number.prototype.toLocaleString()</code> and <code>Date.prototype.toLocaleDateString()</code>.</p>
  174. <p>These methods delegate to three objects: <code>Intl.Collator</code>, <code>Intl.NumberFormat</code>, and <code>Intl.DateTimeFormat</code>. The
  175. collator object enables string comparisons to be language sensitive, while the other two are pretty self-explanatory.</p>
  176. <p>An option of the <code>NumberFormat</code> we took advantage of in our implementation is the <code>style</code>. The style value can be
  177. <code>decimal</code> (default), <code>currency</code>, or <code>percent</code>. In our case, we used both the currency and decimal support for the <code>:c</code> and
  178. <code>:n</code> annotations respectively. For number localization, we also support rounding of fractional digits through the use of
  179. <code>minimumFractionDigits</code> and <code>maximumFractionDigits</code> options.</p>
  180. <h2 id="example-usages">Example usages</h2>
  181. <p>Now, we can translate our original string into different languages by configuring
  182. the <code>I18n</code> object using corresponding locales and message bundle.</p>
  183. <div class="highlight"><pre><code class="javascript"><span class="kd">let</span> <span class="nx">name</span> <span class="o">=</span> <span class="s1">'Bob'</span><span class="p">;</span>
  184. <span class="kd">let</span> <span class="nx">amount</span> <span class="o">=</span> <span class="mf">1234.56</span><span class="p">;</span>
  185. <span class="kd">let</span> <span class="nx">i18n</span><span class="p">;</span>
  186. <span class="kd">let</span> <span class="nx">messageBundle_fr</span> <span class="o">=</span> <span class="p">{</span>
  187. <span class="s1">'Hello {0}, you have {1} in your bank account.'</span><span class="o">:</span> <span class="s1">'Bonjour {0}, vous avez {1} dans votre compte bancaire.'</span>
  188. <span class="p">};</span>
  189. <span class="kd">let</span> <span class="nx">messageBundle_de</span> <span class="o">=</span> <span class="p">{</span>
  190. <span class="s1">'Hello {0}, you have {1} in your bank account.'</span><span class="o">:</span> <span class="s1">'Hallo {0}, Sie haben {1} auf Ihrem Bankkonto'</span>
  191. <span class="p">};</span>
  192. <span class="kd">let</span> <span class="nx">messageBundle_zh_Hant</span> <span class="o">=</span> <span class="p">{</span>
  193. <span class="s1">'Hello {0}, you have {1} in your bank account.'</span><span class="o">:</span> <span class="s1">'你好{0},你有{1}在您的銀行帳戶。'</span>
  194. <span class="p">};</span>
  195. <span class="nx">i18n</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">use</span><span class="p">({</span><span class="nx">locale</span><span class="o">:</span> <span class="s1">'fr-CA'</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="o">:</span> <span class="s1">'CAD'</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="o">:</span> <span class="nx">messageBundle_fr</span><span class="p">});</span>
  196. <span class="nx">i18n</span><span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span><span class="p">;</span>
  197. <span class="c1">// =&gt; 'Bonjour Bob, vous avez 1 234,56 $CA dans votre compte bancaire.'</span>
  198. <span class="nx">i18n</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">use</span><span class="p">({</span><span class="nx">locale</span><span class="o">:</span> <span class="s1">'de-DE'</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="o">:</span> <span class="s1">'EUR'</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="o">:</span> <span class="nx">messageBundle_de</span><span class="p">});</span>
  199. <span class="nx">i18n</span><span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span><span class="p">;</span>
  200. <span class="c1">// =&gt; 'Hallo Bob, Sie haben 1.234,56 € auf Ihrem Bankkonto.'</span>
  201. <span class="nx">i18n</span> <span class="o">=</span> <span class="nx">I18n</span><span class="p">.</span><span class="nx">use</span><span class="p">({</span><span class="nx">locale</span><span class="o">:</span> <span class="s1">'zh-Hant-CN'</span><span class="p">,</span> <span class="nx">defaultCurrency</span><span class="o">:</span> <span class="s1">'CNY'</span><span class="p">,</span> <span class="nx">messageBundle</span><span class="o">:</span> <span class="nx">messageBundle_zh_Hant</span><span class="p">});</span>
  202. <span class="nx">i18n</span><span class="err">`</span><span class="nx">Hello</span> <span class="nx">$</span><span class="p">{</span><span class="nx">name</span><span class="p">},</span> <span class="nx">you</span> <span class="nx">have</span> <span class="nx">$</span><span class="p">{</span><span class="nx">amount</span><span class="p">}</span><span class="o">:</span><span class="nx">c</span> <span class="k">in</span> <span class="nx">your</span> <span class="nx">bank</span> <span class="nx">account</span><span class="p">.</span><span class="err">`</span><span class="p">;</span>
  203. <span class="c1">// =&gt; '你好Bob,你有¥1,234.56在您的銀行帳戶。'</span>
  204. </code></pre></div>
  205. <p>Here’s a link to an <a href="http://www.es6fiddle.net/i0rj2cc9/">ES6 Fiddle</a> for a live demo.</p>
  206. <h2 id="concluding-thoughts">Concluding thoughts</h2>
  207. <p>The tagged template string can be used to provide powerful DSL to JavaScript libraries.
  208. I chose to try my hand at adding simple i18n support. There are still a lot of pieces
  209. missing to provide a comprehensive i18n solution, but I hope to have shown how one
  210. may go about building out this framework.</p>
  211. <p>Pluralization can be a very tricky thing to tackle, and I am not qualified as of this
  212. writing to understand all the nuances of implementing this feature. Perhaps with
  213. a little more thinking, there may be some hope to add it in as well.</p>
  214. <p>In any case, I do see a lot of potential in tagged template strings to add clean, clear
  215. syntax for library functionalities.</p>
  216. <p><small>Edit (2014/03/21): Fixed German translation and added a conclusion section.</small></p>
  217. <p><small>Edit (2014/10/01): Updated examples to not use array comprehension since they were removed in ES6</small></p>