我知道很多次都会问这个问题,但我无法弄清楚我做错了什么
var canvas = document.getElementById('myCanvas');
function handleFiles(files) {
var preview = document.getElementById('preview');
for (var i = 0; i < files.length; i++) {
var file = files[i];
var imageType = /^image\//;
if (!imageType.test(file.type)) {
continue;
}
var img = document.createElement("img");
img.classList.add("obj");
img.src = URL.createObjectURL(file);
preview.appendChild(img); // Assuming that "preview" is the div output where the content will be displayed.
img.onload = drawImage(img);
}
}
var drawImage = function(img) {
var ctx = canvas.getContext("2d");
ctx.drawImage(img, 0, 0);
}
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<div id="preview"></div>
<input type="file" onchange="handleFiles(this.files)">
<canvas id="myCanvas"></canvas>
&#13;
答案 0 :(得分:1)
应该是
img.onload = function(){drawImage(img)};
如果没有方法参数,你可以调用
img.onload = drawImage;
而不是
img.onload = drawImage()// not correct
语法是
x.onload = funcRef;//reference
你应该分配一个函数参考。如果你指定drawImage(img)
,那么drawImage(img)
的返回值将被分配给onload函数