方案一
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title> New Document </title>
</head>
<script src="http://i.gtimg.cn/qzone/biz/gdt/lib/jquery/jquery-2.1.4.js?max_age=31536000"></script>
<script>
$(function(){
$('#upLoad').on('change',function(){
var filePath = $(this).val(), //獲取到input的value，裏面是文件的路徑
fileFormat = filePath.substring(filePath.lastIndexOf(".")).toLowerCase(),
imgBase64 = '', //存儲圖片的imgBase64
fileObj = document.getElementById('upLoad').files[0]; //上傳文件的對象,要這樣寫才行，用jquery寫法獲取不到對象
// 檢查是否是圖片
if( !fileFormat.match(/.png|.jpg|.jpeg/) ) {
alert('上傳錯誤,文件格式必須爲：png/jpg/jpeg');
return;
}
// 調用函數，對圖片進行壓縮
compress(fileObj,function(imgBase64){
imgBase64 = imgBase64; //存儲轉換的base64編碼
$('#viewImg').attr('src',imgBase64); //顯示預覽圖片
});
});
// 不對圖片進行壓縮，直接轉成base64
function directTurnIntoBase64(fileObj,callback){
var r = new FileReader();
// 轉成base64
r.onload = function(){
//變成字符串
imgBase64 = r.result;
console.log(imgBase64);
callback(imgBase64);
}
r.readAsDataURL(fileObj); //轉成Base64格式
}
// 對圖片進行壓縮
function compress(fileObj, callback) {
if ( typeof (FileReader) === 'undefined') {
console.log("當前瀏覽器內核不支持base64圖標壓縮");
//調用上傳方式不壓縮
directTurnIntoBase64(fileObj,callback);
} else {
try {
var reader = new FileReader();
reader.onload = function (e) {
var image = $('<img/>');
image.load(function(){
square = 700, //定義畫布的大小，也就是圖片壓縮之後的像素
canvas = document.createElement('canvas'),
context = canvas.getContext('2d'),
imageWidth = 0, //壓縮圖片的大小
imageHeight = 0,
offsetX = 0,
offsetY = 0,
data = '';
canvas.width = square;
canvas.height = square;
context.clearRect(0, 0, square, square);
if (this.width > this.height) {
imageWidth = Math.round(square * this.width / this.height);
imageHeight = square;
offsetX = - Math.round((imageWidth - square) / 2);
} else {
imageHeight = Math.round(square * this.height / this.width);
imageWidth = square;
offsetY = - Math.round((imageHeight - square) / 2);
}
context.drawImage(this, offsetX, offsetY, imageWidth, imageHeight);
var data = canvas.toDataURL('image/jpeg');
//壓縮完成執行回調
callback(data);
});
image.attr('src', e.target.result);
};
reader.readAsDataURL(fileObj);
}catch(e){
console.log("壓縮失敗!");
//調用直接上傳方式 不壓縮
directTurnIntoBase64(fileObj,callback);
}
}
}
});
</script>
<body>
<input type="file" id="upLoad" name="image" >
<!-- 顯示上傳之後的圖片 -->
<div id='previewImg'>
<img src="" id='viewImg'/>
</div>
</body>
</html>
方案2
<!doctype html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
</head>
<body>
<input type="file"><br>
<img src="" height="200" alt="Image preview area..." title="preview-img">
<script>
var fileInput = document.querySelector('input[type=file]'),
previewImg = document.querySelector('img');
fileInput.addEventListener('change', function () {
var file = this.files[0];
var reader = new FileReader();
// 監聽reader對象的的onload事件，當圖片加載完成時，把base64編碼賦值給預覽圖片
reader.addEventListener("load", function () {
previewImg.src = reader.result;
}, false);
// 調用reader.readAsDataURL()方法，把圖片轉成base64
reader.readAsDataURL(file);
}, false);
</script>
</body>
</html>
轉載於：
https://www.cnblogs.com/xh_Blog/p/8269581.html