var varName = function funcName() {}

Question

What is the difference between

var a = function() {}

and

var a = function b() {}

The latter, b is undefined?

In the latter, b is defined only within the function but should be undefined outside it. The purpose is to allow anonymous functions to recurse. Older Mozilla or IE (don't remember) had a bug where b is not undefined outside the function - but the recursion thing still worked. — slebetman, Oct 03 '13 at 08:57
@Pumbaa80: not duplicate, I've read that topic before ask. Anyway, thanks! — Thịnh Phạm, Oct 03 '13 at 09:01
@Pumbaa80: that's about function expressions vs definitions, which is _slightly_ different than this question. — Qantas 94 Heavy, Oct 03 '13 at 10:37
@Qantas94Heavy I understand that the question is different. Dozens of variations of this have been asked (for example, http://stackoverflow.com/questions/1013385/), but they are all answered in http://stackoverflow.com/a/338053/27862 — user123444555621, Oct 03 '13 at 11:12

score 4 · Answer 1 · edited May 23 '17 at 10:29

4

The second one is a named anonymous function - the name will appear in a stacktrace (otherwise in the stacktrace you''ll see just "anonymous function")

edited May 23 '17 at 10:29

Community

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answered Oct 03 '13 at 08:52

Maxim Krizhanovsky

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Technically its called a named function expression. It's used to implement recursive anonymous functions since you're no longer allowed to use arguments.callee in html5 strict mode – slebetman Oct 03 '13 at 08:55
@Darhazer: Thanks! The latter will return "b" if I print out a.name. – Thịnh Phạm Oct 03 '13 at 09:02
@slebetman: maybe you're thinking of Javascript's strict mode, not html. – Qantas 94 Heavy Oct 03 '13 at 09:02
1

@Qantas94Heavy: Yeah, brainfart on my part, I meant the new javascript strict mode as defined in ES5. – slebetman Oct 03 '13 at 09:04

Qantas 94 Heavy · Answer 2 · 2013-10-03T09:15:53.680

The first is an anonymous function expression and the second a named function expression, both valid in Javascript.

For example, it can be used for recursion without arguments.callee (deprecated and not permitted in strict mode), because it refers to itself, no matter where. The scope of the reference is local only to inside the function, that is it isn't accessible globally:

var a = function b(){
    return b;
 };
function c() {
    return c;
}
var d = function e() {
    return e();
};
d(); // maximum call stack size exceeded :P
var f = c;
c = null;
f(); // null
a(); // function
b();// undefined not a function
b; // not defined
a()(); // same function again

One more thing you forgot from your example: `a()()` which calls the returned "b" (which in this case is itself so it's just a bit silly, but informative nonetheless) — slebetman, Oct 03 '13 at 09:06

score 1 · Answer 3 · edited Oct 03 '13 at 09:24

1

var a = function() {}

Function name can be omitted. In this case function name is omitted. These functions are called anonymous functions.

Read about javascript scope and anonymous function advantages and disadvantages for details.

edited Oct 03 '13 at 09:24

Bridge

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answered Oct 03 '13 at 09:04

Rohit V Jain

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var varName = function funcName() {}

3 Answers3