How do I pass opitional/default parameters in javascript?

Question

function demo(a,b,c,d=1,e=2,f=3){
    console.log(a,b,c,d,e,f); //prints all passed parameters
}

demo(1,2,3,e=5); //calls demo function with the parameter 'e' set to 5

//expected output: 1 2 3 1 5 3

//real output: 1 2 3 5 2 3

JS doesn't have named arguments. You can't skip over arguments like you can in Python. — Barmar, Mar 22 '23 at 19:17
The usual solution for this is for the function to take all the options in a single object parameter. You can then merge the parameter with an object containing defaults. — Barmar, Mar 22 '23 at 19:18
Does this answer your question? [Is there a way to provide named parameters in a function call in JavaScript?](https://stackoverflow.com/questions/11796093/is-there-a-way-to-provide-named-parameters-in-a-function-call-in-javascript) — kelsny, Mar 22 '23 at 19:18
I read that post before I posted my question. The answer by Nina Scholz is the perfect answer for me :) — msba, Mar 22 '23 at 20:07

score 3 · Accepted Answer · answered Mar 22 '23 at 19:19

You need to use the right parameter slot for handing over a value, like

function demo(a, b, c, d = 1, e = 2, f = 3) {
    console.log(a, b, c, d, e, f);
}

demo(1, 2, 3, undefined, 5);

Another solution could be an object, like

function demo({ a, b, c, d = 1, e = 2, f = 3 }) {
    console.log(a, b, c, d, e, f);
}

demo({ a: 1, b: 2, c: 3, e: 5 });

How do I pass opitional/default parameters in javascript?

1 Answers1