Question

I m creating an HTML5 with Javascript, but sometimes the code is executing the next line of statement before the current line is finished,

For example, I m passing an image to an object in Javascript, but then the next statement is executed already before the object has the image, so sometimes the object has no image, but sometimes it has,

So between the 2 lines I need to assign something like callback or wait function, but i dont know how

var image=new Image();
ws.send("complete");

Answer 1

Javascript 是( 主要是) 零星的, 这是件好事。您不想在等待图像时屏蔽 UI 。

在图像完成后执行 ws. send 时使用以下方法执行 :

var image = new Image();
image.onload = function()
{
 ws.send("complete");
}
image.src =  image.jpg ;

如果你这样做同步,整个程序会阻断, 你不想这样做。

至于回调,您可以将函数作为参数传递到函数中。例如:

function doSomething(callback)
{       
    callback();
}

doSomething(function()
{
 console.log( im done! );
});

Answer 2

Not sure if your question is image specific, but for images, you can do the following: The onload event will fire once the image is loaded.

var im = new Image();
im.onload = function() { ws.send( complete ); }
im.src =  path/to/image.jpg

Answer 3

看看这个:

基本上,您必须写出一个事件听筒,在图像装入时能够捕捉事件。

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