JS pass default parameter as a variable that is defined inside that function?

Question

For example:

function mf(z, x c, lol = b) { // I need lol = azazaz
  let b = azazaz
  ...
}

Instead of lol = azazaz I obviously get b is not defined.

What I can do:

function mf(z, x, c, lol = "b") { //parameter lol is a string
  let b = azazaz
  lol = eval(lol) //now lol = azazaz
  ...
}

Also I can do this:

function mf(z, x, c, lol) { //parameter lol doesn't have default value
  b = azazaz
  if (lol == 0) {
    lol = b             //default value of lol = azazaz
  }
  ...
}

But the first one looks so non-professional, the second one has extra if statement which I also don't want. Is there any better way to do this?

function mf(z, x c, lol = 'azazaz') or when you call it like mf(z, x c, 'azazaz') ? — Simone Rossaini
– Simone Rossaini, Commented Mar 31, 2022 at 11:43
function mf(z, x c, lol = 'b') where 'b' contains the result of some actions inside of my function. The 'b' can be 'azazaz' or another value — Max
– Max, Commented Mar 31, 2022 at 11:53

Kanishk Anand · Accepted Answer · 2022-03-31 11:49:05Z

1

If defining the variable inside of the function isn't a hard requirement, you can probably leverage closures to do something like:

const b = 'azazaz';
function mf(z, x, c, lol = b) { 
 ...
}

Or, perhaps use 'OR' to avoid if

function mf(z, x, c, lol) { //parameter lol doesn't have default value
  let b = 'azazaz';
  lol = lol || b;
  ...
}

answered Mar 31, 2022 at 11:49

Kanishk Anand

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2 Comments

3limin4t0r Over a year ago

lol = lol || b could also be written as lol ||= b. See the ||= documentation for details and compatibility.

Kanishk Anand Over a year ago

@3limin4t0r makes sense, thanks for the suggestion :)

Simone Rossaini · Accepted Answer · 2022-03-31 12:00:23Z

0

If you need to change paramater and re-use it you must re-call the function like:

//every time function change lol and recall function
function mf(z, x, c, lol) {
  console.log('lol now is: ' + lol);
  lol++;
  if (lol <= 10) {
    mf(1, 2, 3, lol);
  }
}

mf(1, 2, 3, 0);

answered Mar 31, 2022 at 12:00

Simone Rossaini

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