JavaScript functions equivalency

Question

Can anyone explain to me what the following JavaScript expressions mean? and why they yield different results? How do the following two expressions help anyone differentiate value or reference types in JavaScript?

(function () {}) === (function () {})
//=> false

(function () {})() === (function () {})()
//=> true

this is not "advanced" at all...

tckmn
– tckmn

2014-01-02 16:39:49 +00:00
Commented Jan 2, 2014 at 16:39 — tckmn
– tckmn, Commented Jan 2, 2014 at 16:39
Are you happy with the title now???.

Athapali
– Athapali

2014-01-02 16:43:33 +00:00
Commented Jan 2, 2014 at 16:43 — Athapali
– Athapali, Commented Jan 2, 2014 at 16:43

Evan Davis · Accepted Answer · 2014-01-02 16:39:32Z

5

(function () {}) === (function () {})

Compares two functions. Function equivalence is tricky.

(function () {})() === (function () {})()

Compares the results of two functions, both of which return undefined.

answered Jan 2, 2014 at 16:39

Evan Davis

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5 Comments

Athapali Over a year ago

so (function () {}) is an anonymous self-executing function with no arguments? while the ones in the second expression have arguments for both?

Evan Davis Over a year ago

no, (function() {}) is just a function expression (with no arguments) wrapped in parens. (function() {})() is an IIFE of a function with no arguments.

Athapali Over a year ago

Could I have deleted the wrapper parens to avoid confusion? In first expression? In second expression?

Givi Over a year ago

@SariksaThapa. Since, JavaScript function has no signature it's just objects (instances) that created with Function constructor, there's no difference between function with parameters/arguments and without it. So, 2 instances of Function would be always return false when comparing, since their reference value is different and they refer different location in heap.

Evan Davis Over a year ago

@SariksaThapa yes in the first case, no in the second. The parens are necessary for the function to be invoked immediately. You can, however, put the invoking parens inside or outside the wrapping parens with no change. (function() {}()) === (function() {})()

Andy · Accepted Answer · 2014-01-02 16:40:00Z

0

You create two functions - despite we know they do the same (nothing), those are two different functions.

In the second one we compare returned values - by default - undefined.

answered Jan 2, 2014 at 16:40

Andy

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