upload-images/js/upload_images_controller.js

/*
Resources:
- https://developer.mozilla.org/en-US/docs/Web/API/File/Using_files_from_web_applications
- https://tympanus.net/codrops/2015/09/15/styling-customizing-file-inputs-smart-way/
- https://eloquentjavascript.net/18_http.html
*/

application.register(
    'upload-images',
    class extends Stimulus.Controller {
        static get targets() {
            return ['input', 'output', 'dropzone']
        }

        openFileSelector() {
            this.inputTarget.click()
        }
        addActiveClass(event) {
            event.preventDefault()
            this.dropzoneTarget.classList.add('active')
        }
        removeActiveClass() {
            this.dropzoneTarget.classList.remove('active')
        }

        handleImages(event) {
            event.preventDefault()
            let images = []
            if (event.type == 'change') {
                images = event.target.files
            } else if (event.type == 'drop') {
                images = event.dataTransfer.files
            }
            Array.from(images).forEach(image => {
                const imageName = image.name
                const imageSize = image.size
                const isOversized =
                    Math.round(imageSize / 1024) >
                    Number(this.data.get('maxSizeKb'))

                if (isOversized) {
                    this.outputTarget.classList.add('oversized')
                    this.outputTarget.innerText = `Oversized!`
                    this.inputTarget.value = ''
                    return
                } else {
                    this.outputTarget.classList.remove('oversized')
                    this.dropzoneTarget.classList.add('hidden')
                }

                const figure = document.createElement('figure')

                const img = document.createElement('img')
                img.file = image // Required for future upload, fragile?
                img.src = window.URL.createObjectURL(image)
                img.onload = event =>
                    window.URL.revokeObjectURL(event.target.src)
                img.alt = 'Picture preview'
                figure.appendChild(img)

                const figcaption = document.createElement('figcaption')
                figcaption.innerText = imageName
                figure.appendChild(figcaption)

                this.outputTarget.appendChild(figure)
            })
        }

        submit(event) {
            event.preventDefault()
            const images = this.outputTarget.querySelectorAll('img')
            Array.from(images).forEach(image => {
                const formdata = new FormData()
                formdata.append('images', image.file)
                const options = {
                    method: this.element.method,
                    body: formdata
                }
                console.log(`Uploading "${image.file.name}"`)
                this._request(
                    this.element.action,
                    options,
                    this._displayPercentage
                )
                    .then(response => console.log('Uploaded!'))
                    .catch(console.log.bind(console))
            })
        }

        _request(url, options = {}, onProgress) {
            // See https://github.com/github/fetch/issues/89#issuecomment-256610849
            return new Promise((resolve, reject) => {
                const xhr = new XMLHttpRequest()
                xhr.open(options.method || 'get', url)
                for (let header in options.headers || {})
                    xhr.setRequestHeader(header, options.headers[header])
                xhr.onload = event => resolve(event.target.responseText)
                xhr.onerror = reject
                if (xhr.upload && onProgress) xhr.upload.onprogress = onProgress
                xhr.send(options.body)
            })
        }

        _displayPercentage(event) {
            if (event.lengthComputable) {
                const percentage = Math.round(
                    (event.loaded * 100) / event.total
                )
                console.log(percentage)
            }
        }
    }
)