//base64转码（压缩完成后的图片为base64编码，这个方法可以将base64编码转回file文件）
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function dataURLtoFile(dataurl) {
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let arr, mime, bstr, n, u8arr;
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arr = dataurl.split(',');
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mime = arr[0].match(/:(.*?);/)[1];
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bstr = atob(arr[1]);
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n = bstr.length;
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u8arr = new Uint8Array(n);
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while (n--) {
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u8arr[n] = bstr.charCodeAt(n);
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}
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return new File([u8arr], { type: mime });
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}
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//压缩图片
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function compressImg(file){
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// file = convertBase64UrlToBlob(file.content);
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const name = file.name;
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let files;
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let fileSize = parseFloat(parseInt(file['size'])/1024/1024).toFixed(2);
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let read = new FileReader();
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read.readAsDataURL(file);
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return new Promise(function(resolve){
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read.onload = function (e) {
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let img = new Image();
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img.src = e.target.result;
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img.onload = function(){
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//默认按比例压缩
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let w = this.width,
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h = this.height;
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//生成canvas
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let canvas = document.createElement('canvas');
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let ctx = canvas.getContext('2d');
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let base64;
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// 创建属性节点
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canvas.setAttribute("width", w);
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canvas.setAttribute("height", h);
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ctx.drawImage(this, 0, 0, w, h);
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if(fileSize<1){
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//如果图片小于一兆 那么不执行压缩操作
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base64 = canvas.toDataURL(file['type'], 1);
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}else if(fileSize>1&&fileSize<2){
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//如果图片大于1M并且小于2M 那么压缩0.5
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base64 = canvas.toDataURL(file['type'], 0.5);
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}else{
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//如果图片超过2m 那么压缩0.2
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base64 = canvas.toDataURL(file['type'], 0.2);
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}
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// 回调函数返回file的值（将base64编码转成file）
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files = dataURLtoFile(base64); //如果后台接收类型为base64的话这一步可以省略
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let img = new File([files], name, {
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type: 'image/jpeg',
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});
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//图片大小大于1024*1024，则再次压缩
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if (img.size > 1024*1024) {
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compressImg(img).then(res=>{
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img = res;
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resolve(img)
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})
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}else {
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resolve(img)
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}
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};
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};
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})
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}
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//结尾处将该方法暴露出来供外部调用
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export default {
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compressImg,
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}
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