javascript - for循环中的自调用函数

Question

这是来自 https://github.com/Khan/khan-exercises/blob/master/khan-exercise.js 的代码

for ( var i = 0; i < loading; i++ ) (function( mod ) {
    if ( !testMode && mod.src.indexOf("/khan-exercises/") === 0 && mod.src.indexOf("/MathJax/") === -1 ) {
        // Don't bother loading khan-exercises content in production
        // mode, this content is already packaged up and available
        // (*unless* it's MathJax, which is silly still needs to be loaded)
        loaded++;
        return;
    }

    // Adapted from jQuery getScript (ajax/script.js)
    var script = document.createElement("script");
    script.async = "async";

    for ( var prop in mod ) {
        script[ prop ] = mod[ prop ];
    }

    script.onerror = function() {
        // No error in IE, but this is mostly for debugging during development so it's probably okay
        // http://stackoverflow.com/questions/2027849/how-to-trigger-script-onerror-in-internet-explorer
        Khan.error( "Error loading script " + script.src );
    };

    script.onload = script.onreadystatechange = function() {
        if ( !script.readyState || ( /loaded|complete/ ).test( script.readyState ) ) {
            // Handle memory leak in IE
            script.onload = script.onreadystatechange = null;

            // Remove the script
            if ( script.parentNode ) {
                script.parentNode.removeChild( script );
            }

            // Dereference the script
            script = undefined;

            runCallback();
        }
    };

    head.appendChild(script);
})( urls[i] );

奇怪的事情:我们看到的是自调用函数，而不是通常的 for 循环代码块!(在其他自调用函数内部)为什么会这样？这个函数将如何运行？

Answer 1

基本上，for 循环 每次都会运行该函数，并将值 url[i] 传递到 mod 参数中。

for ( var i = 0; i < loading; i++ ) (function( mod ) {...The code...})(urls[i]);

如果你在代码中注意到，你会看到这个

(function( mod ) {...The code...})(urls[i])

这是一个函数调用，将 urls[i] 传递给参数 mod