图片转base64并压缩大小

html代码

<input id="file" type="file"  capture="microphone" accept="image/*"> 

JavaScript代码 

$("#file").change(function(){
var m_this = this;

      cutImageBase64(m_this,null,400,0.8);  

})

function cutImageBase64(m_this,id,wid,quality) {

    var file = m_this.files[0];

    var URL = window.URL || window.webkitURL;

    var blob = URL.createObjectURL(file);

    var base64;
var img = new Image();

    img.src = blob;

    img.onload = function() {

        var that = this;

        //生成比例

        var w = that.width,

            h = that.height,

            scale = w / h;

            w = wid || w;

            h = w / scale;
//生成canvas

        var canvas = document.createElement('canvas');

        var ctx = canvas.getContext('2d');

        $(canvas).attr({

            width: w,

            height: h

        });

        ctx.drawImage(that, 0, 0, w, h);

        // 生成base64            

        base64 = canvas.toDataURL('image/jpeg', quality || 0.8);
console.log(base64)

    };

}