<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
<title>通过filereader接口读取文件</title>
<script type="text/javascript">
function readAsDataURL()
{
if(typeof FileReader=='undifined') //判断浏览器是否支持filereader
{
result.innerHTML="<p>抱歉，你的浏览器不支持 FileReader</p>";
return false;
}
var file=document.getElementById("imagefile").files[0];
if(!/image/w+/.test(file.type)) //判断获取的是否为图片文件
{
alert("请确保文件为图像文件");
return false;
}
var reader=new FileReader();
reader.readAsDataURL(file);
reader.onload=function(e)
{
var result=document.getElementById("result");
result.innerHTML='<img src="'+this.result+'" alt=""/>'
}
}
</script>
</head>
<body>
<p>
<label>请选择一个文件：</label>
<input type="file" id="imagefile" />
<input type="button" value="读取图像" onClick="readAsDataURL();" />
</p>
<div name="result" id="result">
<!-- 这里用来显示图片结果-->
</div>
</body>
</html>
使用FileReader接口的readAsDataURL方法实现图片的预览。
<template>
<div class="vs-upload">
<div>
<div class="vs-upload__show" v-if="showimg">
<img :src="img" width="100%" >
</div>
<div class="vs-upload__show" v-else>
<div class="vs-upload__picture" :style="'backgroundImage:url('+headerImage+')'"></div>
</div>
<label for="upload" class="vs-upload__select">修改头像</label>
<input type="file" id="upload" accept="image" @change="onUpload" style="margin-left: -999999px;">
</div>
</div>
</template>
<script>
export default {
name: 'v-upload',
props:{
img:'',
id:''
},
data() {
return {
showimg:false,
headerImage: '',
picValue: ''
}
},
created: function() {
if(this.headerImage != null){
this.showimg=true
}else{
this.showimg=false
}
},
mounted() {},
methods: {
onUpload(e) {
this.showimg=false;
let files = e.target.files || e.dataTransfer.files;
if (!files.length) return;
this.picValue = files[0];
this.imgPreview(this.picValue);
},
imgPreview(file) {
let self = this;
let Orientation;
if (!file || !window.FileReader) return;
if (/^image/.test(file.type)) {
let reader = new FileReader();
reader.readAsDataURL(file);
reader.onloadend = function() {
let result = this.result;
let img = new Image();
img.src = result;
if (this.result.length <= (100 * 1024)) {
self.headerImage = this.result;
self.postImg();
} else {
img.onload = function() {
let data = self.compress(img, Orientation);
self.headerImage = data;
self.postImg();
}
}
}
}
},
postImg() {
this.$emit('upload', this.headerImage)
},
rotateImg(img, direction, canvas) {
const min_step = 0;
const max_step = 3;
if (img == null) return;
let height = img.height;
let width = img.width;
let step = 2;
if (step == null) {
step = min_step;
}
if (direction == 'right') {
step++;
step > max_step && (step = min_step);
} else {
step--;
step < min_step && (step = max_step);
}
let degree = step * 90 * Math.PI / 180;
let ctx = canvas.getContext('2d');
switch (step) {
case 0:
canvas.width = width;
canvas.height = height;
ctx.drawImage(img, 0, 0);
break;
case 1:
canvas.width = height;
canvas.height = width;
ctx.rotate(degree);
ctx.drawImage(img, 0, -height);
break;
case 2:
canvas.width = width;
canvas.height = height;
ctx.rotate(degree);
ctx.drawImage(img, -width, -height);
break;
case 3:
canvas.width = height;
canvas.height = width;
ctx.rotate(degree);
ctx.drawImage(img, -width, 0);
break;
}
},
compress(img, Orientation) {
let canvas = document.createElement("canvas");
let ctx = canvas.getContext('2d');
let tCanvas = document.createElement("canvas");
let tctx = tCanvas.getContext("2d");
let initSize = img.src.length;
let width = img.width;
let height = img.height;
let ratio;
if ((ratio = width * height / 4000000) > 1) {
ratio = Math.sqrt(ratio);
width /= ratio;
height /= ratio;
} else {
ratio = 1;
}
canvas.width = width;
canvas.height = height;
ctx.fillStyle = "#fff";
ctx.fillRect(0, 0, canvas.width, canvas.height);
let count;
if ((count = width * height / 1000000) > 1) {
count = ~~(Math.sqrt(count) + 1);
let nw = ~~(width / count);
let nh = ~~(height / count);
tCanvas.width = nw;
tCanvas.height = nh;
for (let i = 0; i < count; i++) {
for (let j = 0; j < count; j++) {
tctx.drawImage(img, i * nw * ratio, j * nh * ratio, nw * ratio, nh * ratio, 0, 0, nw, nh);
ctx.drawImage(tCanvas, i * nw, j * nh, nw, nh);
}
}
} else {
ctx.drawImage(img, 0, 0, width, height);
}
if (Orientation != "" && Orientation != 1) {
switch (Orientation) {
case 6:
this.rotateImg(img, 'left', canvas);
break;
case 8:
this.rotateImg(img, 'right', canvas);
break;
case 3:
this.rotateImg(img, 'right', canvas);
this.rotateImg(img, 'right', canvas);
break;
}
}
let ndata = canvas.toDataURL('image/jpeg', 0.1);
tCanvas.width = tCanvas.height = canvas.width = canvas.height = 0;
return ndata;
},
}
}
</script>
<style>
.vs-upload__show {
100px;
height: 100px;
overflow: hidden;
position: relative;
border-radius: 50%;
border: 1px solid #d5d5d5;
}
.vs-upload__picture {
100%;
height: 100%;
overflow: hidden;
background-position: center center;
background-repeat: no-repeat;
background-size: cover;
}
</style>