Query regarding coding paradigm used in this library.

[simbathesailor]

Why in the code string concatenation is used to create the function? I can see, this approach is being followed in almost every file. Why shouldn't it be written as a normal function? For example like this in HookCodeFactory .

switch(this.options.type) { case "sync": return new Function(this.args(), "\"use strict\";\n" + this.header() + this.content({ onError: err => throw ${err};\n, onResult: result => return ${result};\n, onDone: () => "", rethrowIfPossible: true }));

[ooflorent]

Correct me if I'm wrong but you are wondering why some closures are defined using Function and string concatenations instead of a plain function declaration or expression, right?

Well, this is for optimisation purpose. Defining functions using Function constructor is expensive. However, the code generated by tapable is monomorphic and is crafted to be executed really fast.

[simbathesailor]

@ooflorent First of all thanks for replying . Well You are correct . I am asking the same. I am still not getting any idea, why using Function constructor is expensive. I can read following lines on mdn

Function objects created with the Function constructor are parsed when the function is created. This is less efficient than declaring a function with a function expression or function statement and calling it within your code because such functions are parsed with the rest of the code.

May be I am thinking other way. Could you please elaborate ?

[ooflorent]

Sure! Let's consider the following functions; they are really simple hook factory implementations:

const f = (...fns) => (...args) => {
  for (const fn of fns) {
    fn(...args)
  }
}

const g = (a, b, c) => (x, y) => {
  a(x, y)
  b(x, y)
  c(x, y)
}

Both functions achieve the same thing but g is more specific. While f accepts any number of callbacks and applies any number of arguments on them, g takes 3 callbacks and calls them using 2 arguments. Because g is specialised for this use case, it will perform much better than f.

Keep in mind that tapable is used by webpack. The created hooks can hold dozens of callbacks with multiple arguments depending on the event. Specialised functions like g could not realistically be used to cover all callsites. This is the reason why hooks are generated: this way it is possible to define a specialised version where loops are unrolled to improve performances.

[simbathesailor]

Oh Now I understand, basically the code which is returned is dynamic. so depending on varying number of arguments and other parameters, new functions is being created and returned. In this way, the code length will be dynamic and saves the code length in most cases.

Thanks, @ooflorent. Actually going through webpack code to learn and contribute. You can close the issue !!

[elevenpassin]

What does monomorphic mean? @ooflorent

[ooflorent]

Here is a good explanation: What's up with monomorphism?

[elevenpassin]

Thanks!