Pass the last parameter to function - JavaScript

Question

If I have a function with two different parameters, how can I make it so that if I input only one parameter, it will use the input as the second parameter rather than the first parameter? For example, if I have this function:

function x(a=1,b=2) {
    console.log(a);
    console.log(b);
}

and call x(3), it will use the 3 for a and return "3, 2"

x(3);

=> 3
   2

I want it so that the function instead uses the 3 for the b parameter, and therefore returns "1, 3"

x(3);
=> 1
   3

While this can technically be done, what is your use case? There is almost certainly a better alternative. — Andrew, Nov 27 '20 at 20:44
`x(undefiined, 3)` but if you really want to have any parameter optional, you should probably pass an object. — VLAZ, Nov 27 '20 at 20:44
Very related: [Set a default parameter value for a JavaScript function](https://stackoverflow.com/q/894860) — VLAZ, Nov 27 '20 at 20:46
Does this answer your question? [How to pass the nth optional argument without passing prior arguments in JavaScript functions?](https://stackoverflow.com/questions/57040478/how-to-pass-the-nth-optional-argument-without-passing-prior-arguments-in-javascr) — Ivar, Nov 27 '20 at 20:48
Thank you all, but is there any other way to achieve this than passing parameters as object — Nazeh Taha, Nov 27 '20 at 20:56

Jamiec · Accepted Answer · 2020-11-27T20:54:02.693

2

If you change your method to use a destructured object, you can pass an object with just the properties you wish to and default the rest

function x({a=1,b=2} = {}){
  console.log("a",a);
  console.log("b",b);
}

x();
x({a:10})
x({b:20})

edited Nov 27 '20 at 20:54

answered Nov 27 '20 at 20:47

Jamiec

133,658
13
134
193

2

`function x({a=1,b=2} = {})` to allow calling `x()` without anything. – VLAZ Nov 27 '20 at 20:50
Thank you all, but is there any other way to achieve this than passing parameters as object – Nazeh Taha Nov 27 '20 at 20:59
That's like asking if we can define a variable without using `var` or `let`. – technophyle Nov 27 '20 at 21:00

score 0 · Answer 2 · answered Nov 27 '20 at 21:08

0

Use object destructuring approach

let a,b; 

/*
* define variable to avoid overwrite in large application
*/

function x({a=1,b=2} = {}){
  console.log( { a } );
  console.log( { b } );
}

x({b:20}) /* Passed only 'b' here */

answered Nov 27 '20 at 21:08

GMKHussain

3,342
1
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Pass the last parameter to function - JavaScript

2 Answers2