主要依赖了一个compress.js的文件，文件内容如下:
```
/*
* Tencent is pleased to support the open source community by making WeUI.js available.
*
* Copyright (C) 2017 THL A29 Limited, a Tencent company. All rights reserved.
*
* Licensed under the MIT License (the "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://opensource.org/licenses/MIT
*
* Unless required by applicable law or agreed to in writing, software distributed under the License is
* distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
* either express or implied. See the License for the specific language governing permissions and
* limitations under the License.
*//**
* 检查图片是否有被压扁，如果有，返回比率
* ref to http://stackoverflow.com/questions/11929099/html5-canvas-drawimage-ratio-bug-ios
*/function detectVerticalSquash(img) {
// 拍照在IOS7或以下的机型会出现照片被压扁的bug
var data;
var ih = img.naturalHeight;
var canvas = document.createElement('canvas');
canvas.width = 1;
canvas.height = ih;
var ctx = canvas.getContext('2d');
ctx.drawImage(img, 0, 0);
try {
data = ctx.getImageData(0, 0, 1, ih).data;
} catch (err) {
console.log('Cannot check verticalSquash: CORS?');
return 1;
}
var sy = 0;
var ey = ih;
var py = ih;
while (py > sy) {
var alpha = data[(py - 1) * 4 + 3];
if (alpha === 0) {
ey = py;
} else {
sy = py;
}
py = (ey + sy) >> 1; // py = parseInt((ey + sy) / 2)
}
var ratio = (py / ih);
return (ratio === 0) ? 1 : ratio;}/**
* dataURI to blob, ref to https://gist.github.com/fupslot/5015897
* @param dataURI
*/function dataURItoBuffer(dataURI){
var byteString = atob(dataURI.split(',')[1]);
var buffer = new ArrayBuffer(byteString.length);
var view = new Uint8Array(buffer);
for (var i = 0; i < byteString.length; i++) {
view[i] = byteString.charCodeAt(i);
}
return buffer;}function dataURItoBlob(dataURI) {
var mimeString = dataURI.split(',')[0].split(':')[1].split(';')[0];
var buffer = dataURItoBuffer(dataURI);
return new Blob([buffer], {type: mimeString});}/**
* 获取图片的orientation
* ref to http://stackoverflow.com/questions/7584794/accessing-jpeg-exif-rotation-data-in-javascript-on-the-client-side
*/function getOrientation(buffer){
var view = new DataView(buffer);
if (view.getUint16(0, false) != 0xFFD8) return -2;
var length = view.byteLength, offset = 2;
while (offset < length) {
var marker = view.getUint16(offset, false);
offset += 2;
if (marker == 0xFFE1) {
if (view.getUint32(offset += 2, false) != 0x45786966) return -1;
var little = view.getUint16(offset += 6, false) == 0x4949;
offset += view.getUint32(offset + 4, little);
var tags = view.getUint16(offset, little);
offset += 2;
for (var i = 0; i < tags; i++)
if (view.getUint16(offset + (i * 12), little) == 0x0112)
return view.getUint16(offset + (i * 12) + 8, little);
}
else if ((marker & 0xFF00) != 0xFF00) break;
else offset += view.getUint16(offset, false);
}
return -1;}/**
* 修正拍照时图片的方向
* ref to http://stackoverflow.com/questions/19463126/how-to-draw-photo-with-correct-orientation-in-canvas-after-capture-photo-by-usin
*/function orientationHelper(canvas, ctx, orientation) {
const w = canvas.width, h = canvas.height;
if(orientation > 4){
canvas.width = h;
canvas.height = w;
}
switch (orientation) {
case 2:
ctx.translate(w, 0);
ctx.scale(-1, 1);
break;
case 3:
ctx.translate(w, h);
ctx.rotate(Math.PI);
break;
case 4:
ctx.translate(0, h);
ctx.scale(1, -1);
break;
case 5:
ctx.rotate(0.5 * Math.PI);
ctx.scale(1, -1);
break;
case 6:
ctx.rotate(0.5 * Math.PI);
ctx.translate(0, -h);
break;
case 7:
ctx.rotate(0.5 * Math.PI);
ctx.translate(w, -h);
ctx.scale(-1, 1);
break;
case 8:
ctx.rotate(-0.5 * Math.PI);
ctx.translate(-w, 0);
break;
}}/**
* 压缩图片
*/function compress(file, options, callback) {
const reader = new FileReader();
reader.onload = function (evt) {
if(options.compress === false){
// 不启用压缩 & base64上传 的分支，不做任何处理，直接返回文件的base64编码
file.base64 = evt.target.result;
callback(file);
return;
}
// 启用压缩的分支
const img = new Image();
img.onload = function () {
const ratio = detectVerticalSquash(img);
const orientation = getOrientation(dataURItoBuffer(img.src));
const canvas = document.createElement('canvas');
const ctx = canvas.getContext('2d');
const maxW = options.compress.width;
const maxH = options.compress.height;
let w = img.width;
let h = img.height;
let dataURL;
if(w < h && h > maxH){
w = parseInt(maxH * img.width / img.height);
h = maxH;
}else if(w >= h && w > maxW){
h = parseInt(maxW * img.height / img.width);
w = maxW;
}
canvas.width = w;
canvas.height = h;
if(orientation > 0){
orientationHelper(canvas, ctx, orientation);
}
ctx.drawImage(img, 0, 0, w, h / ratio);
if(/image/jpeg/.test(file.type) || /image/jpg/.test(file.type)){
dataURL = canvas.toDataURL('image/jpeg', options.compress.quality);
}else{
dataURL = canvas.toDataURL(file.type);
}
if(options.type == 'file'){
if(/;base64,null/.test(dataURL) || /;base64,$/.test(dataURL)){
// 压缩出错，以文件方式上传的，采用原文件上传
console.warn('Compress fail, dataURL is ' + dataURL + '. Next will use origin file to upload.');
callback(file);
}else{
let blob = dataURItoBlob(dataURL);
blob.id = file.id;
blob.name = file.name;
blob.lastModified = file.lastModified;
blob.lastModifiedDate = file.lastModifiedDate;
callback(blob);
}
}else{
if(/;base64,null/.test(dataURL) || /;base64,$/.test(dataURL)){
// 压缩失败，以base64上传的，直接报错不上传
options.onError(file, new Error('Compress fail, dataURL is ' + dataURL + '.'));
callback();
}else{
file.base64 = dataURL;
callback(file);
}
}
};
img.src = evt.target.result;
};
reader.readAsDataURL(file);}export default {
compress};
```
文件中有多种bug处理，如，拍照在IOS7或以下的机型会出现照片被压扁的bug 、修正拍照时图片的方向、压缩图片等问题。
具体使用也大概说明一下，下例子使用用的是vue-cli
1, 引入 js 注在静态文件目录下，es6引入，，注意，导出的是对象，，且用的是default导出
import compress from '@/assets/js/compress.js'
2, 下面是个人的使用方式，
```
<template>
<div class="course-picture input_file_wrapper flex-center icon-default-img">
<input type="file" @change="handleFile" name="file" class="input_file">
<span class="course-picture-con" :style="{'background-image':'url('+logoImg+')'}"></span>
</div></template><script>import compress from '@/assets/js/exif/compress.js'
export default {
data(){
return {
logoImg : ''
}
},
props : {
logo : {
type : String,
default : ''
},
},
watch :{
logo(val){
this.logoImg = val
}
},
components : {
},
methods : {
// 选择修改图片事件
handleFile(e) {
e.stopPropagation()
let _this = this
let file = e.target.files[0];
if (!/image/w+/.test(file.type)) {
this.$toast('请选择图片')
return
}
compress.compress(file,{
compress: {
width:520,
height:520
}
},function (data) {
_this.logoImg = data.base64
_this.$emit('change',_this.logoImg)
})
},
}
}
</script><style scoped>.course-picture {height: 2.5rem;width: 2.5rem;}</style>
```
说到这儿，懂些vue的大概就知道了，上面是一个当成组件的封装，还可以更完善，谢谢点赞。
来自 “ ITPUB博客 ” ，链接：https://blog.itpub.net/3402/viewspace-2826050/ ，如需转载，请注明出处，否则将追究法律责任。
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