Performance testing of anonymous named functions in JavaScript

We often write callbacks via Anonymous function.

Simply put, anonymous is a function that has no name and is usually executed immediately. But how does it perform with named functions (functions with names)?

Let's compare that. Let's take a random computer that can execute Shell commands and use a lot of function calls.

Anonymous. Js

var count = 100000000

  , sum   = 0

while (count--) (function() { sum++ })()

To perform a

$ time node anonymous.js

real    0m1.456s

user    0m0.015s

sys     0m0.031s

Let's look at the naming function

Named. Js

var count = 100000000

  , sum   = 0
var cb = function() {

  sum++

}
while (count--) cb()

To perform a

$ time node named.js

real    0m0.575s

user    0m0.000s

sys     0m0.046s

Naming functions is a lot faster. Why is that? It's not hard to explain. Anonymous functions need to reinterpret callbacks every time, but named functions only need to be reinterpreted once, so there's a performance boost.

In addition, there are two ways to write named functions:

Functional expression

var func = function() {

  console.log('a')

}

Function declaration

function func() {

  console.log('b')

}

In fact, there may be problems when these two are used together, such as

var func = function() {

  console.log('a')

}

function func() {

  console.log('b')

}

//The output is: a

So we use function expressions a lot, but what about the performance of function declarations?

Named2. Js

var count = 100000000

  , sum   = 0
function cb() {

  sum++

}
while (count--) cb()

Execute and compare the two

$ time node named.js

real    0m0.553s

user    0m0.000s

sys     0m0.015s
$ time node named2.js

real    0m0.529s

user    0m0.000s

sys     0m0.047s

It seems like the function declaration is going to be a little bit faster, but it's not too fast and it's not very, very obvious.

PS: this data is all tested with git-base under Windows7.