Defaulting variable value if parameter type mismatch, in JavaScript

Question

I have a function with an optional parameter. I'm defaulting the value to 1000 if the parameter isn't supplied like so:

function zoom( coords, zoomSpeed){
  zoomSpeed = zoomSpeed || 1000;
  //rest of code
}

This works for testing presence of the parameter, but I also want to make sure a number was supplied as the parameter. I'm using the following but it seems like there is a better way to do this.

function zoom( coords, zoomSpeed){
  if (typeof zoomSpeed === "number"){
    zoomSpeed = zoomSpeed;
  }else{
    zoomSpeed = 1000;
  }
  //rest of code
}

Any feedback on a better way to do this would be appreciated.

What if somebody passes in the string "100". Is that okay? – Raymond Chen Sep 28 '15 at 18:49 — Raymond Chen, Sep 28 '15 at 18:49

Simon H · Answer 1 · 2015-09-28T15:30:06.783

4

This is shorter:

if (typeof zoomSpeed !== "number"){
    zoomSpeed = 1000;
}

edited Sep 28 '15 at 15:30

answered Sep 28 '15 at 15:18

Simon H

20,332
14
71
128

marekful · Accepted Answer · 2015-09-28T18:16:17.287

2

... or

zoomSpeed = parseInt(zoomSpeed) || 1000

edited Sep 28 '15 at 18:16

answered Sep 28 '15 at 15:19

marekful

14,986
6
37
59

`zoomSpeed = +zoomSpeed || 0;` – Jared Smith Sep 28 '15 at 15:21
Should be `|| 1000` and hopefully the value can not be zero passed in. – epascarello Sep 28 '15 at 15:22
if `defaultValue = 1000` and `zoomSpeed = 0` result will equal defaultValue. (`zoomSpeed = 1000` not `0`) – Sherali Turdiyev Sep 28 '15 at 16:01
Of course I meant `|| 1000`, corrected and yes, it does not handle the case when the desired input value is zero, that's true. – marekful Sep 28 '15 at 18:16

Sherali Turdiyev · Answer 3 · 2015-09-28T15:38:48.287

0

You can use your zoom(..., "5") through following code

function zoom( coords, zoomSpeed){
  zoomSpeed = Number(zoomSpeed) !== NaN ? Number(zoomSpeed): 1000;
  //... 
}

edited Sep 28 '15 at 15:38

answered Sep 28 '15 at 15:30

Sherali Turdiyev

1,745
16
29

Also, there is other version http://stackoverflow.com/q/9716468/4365315, http://stackoverflow.com/questions/18082/validate-decimal-numbers-in-javascript-isnumeric – Sherali Turdiyev Sep 28 '15 at 15:33
or, just use this `zoomSpeed = Number(zoomSpeed) || 1000;` – Sherali Turdiyev Sep 28 '15 at 15:34

Defaulting variable value if parameter type mismatch, in JavaScript

3 Answers3