export function compress (fileObj, callback) {
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try {
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const image = new Image()
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image.src = URL.createObjectURL(fileObj)
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image.onload = function () {
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const that = this
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// 默认按比例压缩
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let w = that.width
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let h = that.height
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const scale = w / h
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w = fileObj.width || w
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h = fileObj.height || (w / scale)
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let quality = 0.7 // 默认图片质量为0.7
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// 生成canvas
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const canvas = document.createElement('canvas')
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const ctx = canvas.getContext('2d')
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// 创建属性节点
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const anw = document.createAttribute('width')
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anw.nodeValue = w
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const anh = document.createAttribute('height')
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anh.nodeValue = h
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canvas.setAttributeNode(anw)
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canvas.setAttributeNode(anh)
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ctx.drawImage(that, 0, 0, w, h)
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// 图像质量
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if (fileObj.quality && fileObj.quality <= 1 && fileObj.quality > 0) {
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quality = fileObj.quality
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}
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// quality值越小，所绘制出的图像越模糊
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const data = canvas.toDataURL('image/jpeg', quality)
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// 压缩完成执行回调
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const newFile = convertBase64UrlToBlob(data)
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callback(newFile)
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}
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} catch (e) {
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console.log('压缩失败!')
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}
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}
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function convertBase64UrlToBlob (urlData) {
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const bytes = window.atob(urlData.split(',')[1]) // 去掉url的头，并转换为byte
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// 处理异常,将ascii码小于0的转换为大于0
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const ab = new ArrayBuffer(bytes.length)
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const ia = new Uint8Array(ab)
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for (let i = 0; i < bytes.length; i++) {
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ia[i] = bytes.charCodeAt(i)
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}
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return new Blob([ab], { type: 'image/png' })
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}
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