无法为image.onload（）中的范围变量赋值

Question

这就是我所拥有的：

samplepool <- rep(names(q), q)  

当我var test = ''; var img = new Image(); img.src = 'https://blahblah'; img.onload = function () { test = 'Sam'; } 时，它什么也没有显示。如何为console.log(test)内的test分配值？

Answer 1

请参阅此jsFiddle：https://jsfiddle.net/y7Lnp6q1/1/

这取决于你在哪里做console.log。请参阅以下代码中的我的评论：

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.