懒需要解释吗？
function compressedPicture (url, callback) {
var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
var img = new Image;
img.onload = function(){
console.log(img.width);
var width = img.width;
var height = img.height;
// 按比例压缩4倍
var rate = (width < height ? width / height : height / width) / 4;
canvas.width = width * rate;
canvas.height = height * rate;
ctx.drawImage(img, 0, 0, width, height, 0, 0, width * rate, height * rate);
var dataURL = canvas.toDataURL('image/jpeg');
callback.call(this, dataURL);
canvas = null;
console.log(dataURL);
};
img.src = url
}
//调用
this.compressedPicture(这里放base64的图, _ => {
console.log(_);
})
