JavaScript Callback & Closure

Callback

$("button").click(function () {    $("Selector").toggle(5000); // jQuery.toggle();    console.log("this will appear before toggle effect finished");});

$("button").click(function () {    $("Selector").toggle(5000, function(){        // this is a callback function        console.log("this will appear after toggle effect 100% finished");    });});

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Closure

function foo() {    var a = 1;    return function () {        a = a * 2;        return a;    };}var f = foo();console.log(f()); // return 2console.log(f()); // return 4

JavaScript 中没有块儿级作用域，函数运行在定义它们的作用域中，而不是调用它们时所在的作用域。