What is the reason behind JavaScript's `fn.length` returning the count of named parameters that `fn` function has?

Why does calling fn.length in JavaScript return the number of named arguments fn has?

> function fn () { }
> x.length
0

> function fn (a) { }
> x.length
1

> function fn (a,b,c) { }
> x.length
3

This behavior is quite peculiar. I wonder what the explanation behind it is.

Answer №1

According to MDN's guide:

The length attribute represents the expected number of arguments for a function.

Referencing Microsoft's information:

This property retrieves the quantity of arguments specified within a function.

As per the ECMAScript 2015 specification:

The length value is an integer indicating the typical number of expected arguments for the function.

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