Avoiding nested anonymous functions is good for more reasons than listed in the article. The article lists closures holding references to the closed-over variables as being a source of wasted memory. Another point is the fact that anonymous variables require memory allocation each time they are created:
// Uses more memory:
Foo.prototype.someFunction = function () {
;[2, 5, 9].forEach(function (element, index, array) {
console.log("a[" + index + "] = " + element)
})
}
The function will be created every time the outer forEach loop is called.
// Uses less memory:
Foo.prototype.logArrayElements = function (element, index, array) {
console.log("a[" + index + "] = " + element)
}
Foo.prototype.someFunction = function () {
;[2, 5, 9].forEach(this.logArrayElements)
}
Save your created functions for later to save memory.
In both examples, the function is only allocated once, no matter how it's instantiated.
Where you have to be careful is if you have a function that's being called repeatedly and it contains a function instantiation -- that function will be reallocated each time.
[1,2,3].forEach(function(x) {
return (function(a, b) { return a * b })(x, 2)
})
Will repeatedly allocate that inner multiplication function, vs:
mul = function(a, b) { return a * b }
;[1,2,3].forEach(function(x) {
return mul(x, 2)
})
Will only allocate that multiplication function once.
I think we are in complete agreement. Your example is a little prettier however you still have this "unoptimized" line:
;[1,2,3].forEach(function(x) {
If this line is executed more than once, the nested function will be created again and again, wasting memory. However, some people may see my advice here as a micro-optimization. Thus, don't make your code ugly until you identify the real-world bottlenecks. I have updated my code in the grand-parent comment to explain myself a little more clearly (maybe)...
Why an expression and not simply `function logArrayElements`? If you do the latter you'll see more information if you wanted to introspect (toString on the function, or in an error traceback).
