何时在javascript中使用闭包？

Question

I came across a custom filter used in angularJS where we are returning a function with a logic for custom filter. Here I'm not able to understand when exactly i should be using closures. I tried to return a function with in a jquery call back function, but the control just doesn't go inside the function body, but the control goes inside the angularJS custom filter. Can someone help me understand the concept.

AngularJS Custom filter Code, where the control goes inside the anonymous function:

app.filter('myFilter', function () {
    return function (curItem, txtSearch) {
        var results = [];
        if (txtSearch && curItem) {
            for (i = 0; i < curItem.length; i++) {
                // some logic for filter
            }
            return results;

            app.filter('myFilter', function () {
                return function (curItem, txtSearch) {
                    var results = [];
                    if (txtSearch && curItem) {
                        for (i = 0; i < curItem.length; i++) {
                            alert(curItem[i].name);
                        }
                        return results;
                    }
                }
            });}}});

Jquery function where i'm trying to pass the control with in the return anonymous function although i know like i will be able to do with in just the call back instead of using the closure.

$('div').on('click', function () {
    return function () {
        alert('');
    }
});

Answer 1

I suggest you should first understand what closures are before trying to use them. I recommend reading You-Dont-Know-JS book on GitHub for getting clarity on this topic. It is very neatly and conceptually explained in this chapter.

After understanding what closures are and what are their advantages, you can yourself identify the situations where to apply it.

Hope it helps!