无法将值分配给 image.onload() 中的范围外变量

Question

这是我所拥有的：

var test = '';
var img = new Image();
img.src = 'https://blahblah';
img.onload = function () {
    test = 'Sam';
}

当我console.log(test)时，它什么也没显示。如何在onload内部为test赋值？

Answer 1

看到这个jsFiddle： https://jsfiddle.net/y7Lnp6q1/1/

这取决于您在哪里进行控制台.log。请参阅以下代码中的注释：

var test = "";
var img = new Image();
img.src = 'https://developers.google.com/search/docs/data-types/images/recipes01.png';
img.onload = function () {
    test = "Sam";
    console.log("test = " + test); // Will output "test = Sam"
}
console.log("test = " + test); // Will output "test = ", because onload is not yet triggered by this time.