Change Values of All Variables Named via Function Signature

Question

Let say I have a function that has 50 arguments, and I need to modify the values of each named-variable that was created inside the function's signature.

Instead of 50 arguments, he's an example with just 4:

// Each of these strings are padded with intentional and unnecessary whitespace:
let show = "  show ";
let me = " me  ";
let the = " the ";
let bunny = "  bunny   ";

function showMeTheBunny(show, me, the, bunny)
{
	// I want to trim each argument, without having to do this:
	show = show.trim();
	me = me.trim();
	the = the.trim();
	bunny = bunny.trim();
	// The above lines, within this function,
	// are the ones I want to replace with a loop (if possible)

	return `${show} ${me} ${the} ${bunny}: 🐇`; 
}
console.log(showMeTheBunny(show, me, the, bunny)); // output: "show me the bunny: 🐇"

The arguments object can access all the arguments passed into a function, but it doesn't seem to offer a way to change the values of the named-variables themselves.

Is it possible to run all the named-variables (named within a function signature) through a function that modifies each of them before consuming those modified arguments later (using the same variable names)?

Answer 1

You've said you want to modify the values of the "named variables" so I assume you mean the formal parameters (show, me, etc.)

The arguments object can access all the arguments passed into a function, but it doesn't seem to offer a way to change the values of the named-variables themselves.

It does, but only in loose mode, not strict mode:

function showMeTheBunny(show, me, the, bunny)
{
    for (let n = 0; n < arguments.length; ++n)
    {
        arguments[n] = arguments[n].trim();
    }
    return `${show} ${me} ${the} ${bunny}: 🐇`;
}

In that, arguments[0] = arguments[0].trim() updates the value of the show formal parameter, arguments[1] = arguments[1].trim() updates me, etc. But only in loose mode. In strict mode, only arguments[x] would be updated, not the formal parameter; the link back to it is removed. (It's worth noting that strict mode is the default in modules and class constructs.)

Live Example:

// Each of these strings are padded with intentional and unnecessary whitespace:
let show = "  show ";
let me = " me  ";
let the = " the ";
let bunny = "  bunny   ";

function showMeTheBunny(show, me, the, bunny)
{
    for (let n = 0; n < arguments.length; ++n)
    {
        arguments[n] = arguments[n].trim();
    }
	return `${show} ${me} ${the} ${bunny}: 🐇`;
}
console.log(showMeTheBunny(show, me, the, bunny)); // output: "show me the bunny"

There are other ways, but they wouldn't modify the values of the formal parameters. For instance, you could use a rest parameter:

function showMeTheBunny(...rest)
{
    rest = rest.map(entry => entry.trim());
    const [show, me, the, bunny] = rest;
    return `${show} ${me} ${the} ${bunny}: 🐇`;
}

Live Example:

"use strict";
// Each of these strings are padded with intentional and unnecessary whitespace:
let show = "  show ";
let me = " me  ";
let the = " the ";
let bunny = "  bunny   ";

function showMeTheBunny(...rest)
{
    rest = rest.map(entry => entry.trim());
    const [show, me, the, bunny] = rest;
	return `${show} ${me} ${the} ${bunny}: 🐇`;
}
console.log(showMeTheBunny(show, me, the, bunny)); // output: "show me the bunny"

That works in strict mode.

Another option is to accept an object with properties for the parameters, then (again) use destructuring to get individual variables:

function showMeTheBunny(args)
{
    for (const [name, value] of Object.entries(args)) {
        args[name] = value.trim();
    }
    const {show, me, the, bunny} = args;
    return `${show} ${me} ${the} ${bunny}: 🐇`;
}

Live Example:

"use strict";
// Each of these strings are padded with intentional and unnecessary whitespace:
let show = "  show ";
let me = " me  ";
let the = " the ";
let bunny = "  bunny   ";

function showMeTheBunny(args)
{
    for (const [name, value] of Object.entries(args)) {
        args[name] = value.trim();
    }
    const {show, me, the, bunny} = args;
	return `${show} ${me} ${the} ${bunny}: 🐇`;
}
console.log(showMeTheBunny({show, me, the, bunny})); // output: "show me the bunny"

That also works in strict mode.