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HTML5 combined with canvas to achieve image compression

零到壹度Original: 2018-03-24 16:36:031888browse

This time I will bring you HTML5 combined with canvas to achieve image compression, which is mainly reflected in the form of code. The following is a practical case, let's take a look.

<!DOCTYPE html>
<html>
<head>
 <meta charset="UTF-8">
 <meta name=&#39;viewport&#39; content=&#39;width=device-width, initial-scale=1, maximum-scale=1&#39;>
 <title>lianxi </title>
 <style type="text/css">
    </style>
</head>
<body>
    <form>
 名字：<input type="text " name = &#39;username&#39; id = &#39;username&#39;/>
 上传：<input type="file" name = &#39;fileimage&#39; id = &#39;fileimage&#39; />
 </form>
 <button>button</button>
 <script>
 var file = document.querySelector(&#39;#fileimage&#39;)
 var username = document.querySelector(&#39;#username&#39;)
 var canvas = document.createElement(&#39;canvas&#39;);
 var span = document.createElement(&#39;span&#39;)
 var formData = new FormData()
 file.addEventListener(&#39;change&#39;,function() {
 //实现的原理的new formData()然后把这个formData 用ajax传进去
 span.innerHTML = &#39;预览图加载中...&#39;
 document.body.appendChild(span)
 console.log(file.files[0])
 username.value ? formData.append(&#39;username&#39;,username.value) : null;
 resize(file.files[0]);
 })
 //上传前的图片压缩
 function resize(file) {
 var reader = new FileReader()
 reader.readAsDataURL(file)
 var img = new Image()
 reader.onload = function (e) {
 // this.result就是图片的base64地址信息
 img.src = this.result;
 }
 
 var context = canvas.getContext(&#39;2d&#39;);
 var gif = document.createElement(&#39;img&#39;)
 
 // base64地址图片加载完毕后
 img.onload = function () {
 // 图片原始尺寸
 //定义画布的大小
 if (img.width > 300 || img.height > 300) {
 if (img.width > img.height) {
 canvas.width = 300
 canvas.height = img.height / img.width * 300
 }
 else {
 canvas.height = 300
 canvas.width = img.width / img.height * 300
 }
 }
 //从那里开始截取图片
 context.drawImage(img, 0, 0, canvas.width, canvas.height)
 /*第一个参数是创建的img对象；第二个参数是左上角坐标，后面两个是画布区域宽高*/
 //压缩后的图片base64 url
                /*canvas.toDataURL(mimeType, qualityArgument),mimeType 默认值是&#39;image/jpeg&#39;;
                 * qualityArgument表示导出的图片质量，只要导出为jpg和webp格式的时候此参数才有效果，默认值是0.92*/
 //var newUrl = canvas.toDataURL(&#39;image/jpeg&#39;, 0.92);//base64 格式
 document.body.removeChild(span)
 document.querySelector(&#39;body&#39;).appendChild(canvas)
 };
 }
 //这是上传的
 document.querySelector(&#39;button&#39;).addEventListener(&#39;click&#39;,function(){
 canvas.toBlob(function(blob){
 var xhr = new XMLHttpRequest()
 formData.append(&#39;fileimage&#39;, blob,&#39;002.webp&#39;)
 xhr.open(&#39;POST&#39;, &#39;test.php&#39;, true)//默认true 为异步
 //上传进度
 xhr.upload.addEventListener(&#39;progress&#39;,function (e) {
 console.log(&#39;上传进度为：&#39;+ (e.loaded/e.total*100).toFixed(2)+&#39;%&#39;)//多次出现
 // event.total是需要传输的总字节，event.loaded是已经传输的字节
 })
 xhr.upload.addEventListener(&#39;loadstart&#39;, function () {
 console.log(&#39;上传开始&#39;)//只出现一次
 })
 xhr.onreadystatechange = function () {
 if (xhr.readyState === 4) {
 if (xhr.status >= 200 && xhr.status <300 || xhr.status == 304) {
 console.log(JSON.parse(xhr.responseText))//成功后的返回值
 }
 else {
 console.log("Request was unsuccessful: " + xhr.status);
 } 
 }
 
 }
 //xhr.setRequestHeader("Content-type", "multipart/form-data");
 xhr.send(formData)
 }, &#39;image/webp&#39;,0.9)
 })
 </script>
</body>
</html>

It should be noted that the backend needs to add header("Access-Control-Allow-Origin:*"); to achieve cross-domain

HTML5 combined with canvas to achieve image compression

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