拖拽读取文件。之前写的，摘出来做备份

drag&drop file.js

var dropbox = $$("#canvas")[0];
dropbox.ondragenter = function (e) {
    e.preventDefault();
    dropbox.innerHTML = "松开鼠标";
}
dropbox.ondragleave = function (e) {
    e.preventDefault();
    dropbox.innerHTML = "图片拖放至此";
}
dropbox.ondragover = function (e) {
    e.preventDefault();
}
dropbox.ondrop = function (e) {
    e.preventDefault();
    init(e.dataTransfer.files)
}
 
function init (files) {
    if (files.length ==0 || files[0].type.indexOf("image") == -1) {
        return
    };
    var fr = new FileReader();
    var t = fr.readAsDataURL(files[0])
    fr.onload = function (e) {
        var img = new Image();
        img.src = fr.result;
        img.onload = function () {
        }
        
    }
    
}