返回表达式后定义函数的使用场景或优点是什么

Question

En example can be found in Twitter'a typeahead.js here :

function () {
    // ...
    return this.each(initialize);
    function initialize() {
        // ...
    }
}

Questions:

• What are the scopes and what function sees what?
• What is the reason for using such a construct (usage scenarios and advantages)?

Answer 1

Javascript has function based scope, which means that every thing defined inside a function is available from the first line, since the definition is "hoisted" by the complier.

That goes for both variable and function definitions - variable values however, are not available until after assignment.

You can read all about javascript scoping and hoisting here

This means that the function initialize is available from the first line of the wrapping anonymous function.

There is no real reason, and no advantages, for doing it that way, unless you count the code structure as an advantage.

Answer 2

Personally I don't see any reason to do this. For me even it looks a little bit weird. Martin is right. You should be careful, because the defined variables are not accessible like functions. For example this doesn't work:

var getValue = function(func) {
    return func();
}
var f = function() {
    return getValue(now);
    var now = function() {
        return 10;
    }
}

alert(f());

However, this works:

var getValue = function(func) {
    return func();
}
var f = function() {
    return getValue(now);
    function now() {
        return 10;
    }
}

alert(f());