HTML5在上传前预先调整图片大小

This Mozilla Hacks blog post引导您完成大部分的过程。参考这里是源自博客文章的源代码：@H_450_3@

// from an input element
var filesToUpload = input.files;
var file = filesToUpload[0];

var img = document.createElement("img");
var reader = new FileReader();  
reader.onload = function(E) {img.src = e.target.result}
reader.readAsDataURL(filE);

var ctx = canvas.getContext("2d");
ctx.drawImage(img,0);

var MAX_WIDTH = 800;
var MAX_HEIGHT = 600;
var width = img.width;
var height = img.height;

if (width > height) {
  if (width > MAX_WIDTH) {
    height *= MAX_WIDTH / width;
    width = MAX_WIDTH;
  }
} else {
  if (height > MAX_HEIGHT) {
    width *= MAX_HEIGHT / height;
    height = MAX_HEIGHT;
  }
}
canvas.width = width;
canvas.height = height;
var ctx = canvas.getContext("2d");
ctx.drawImage(img,width,height);

var dataurl = canvas.toDataURL("image/png");

//Post dataurl to the server with AJAX