How do I set the default value for an optional argument in Javascript?

Question

I am writing a Javascript function with an optional argument, and I want to assign the optional argument a default value. How can I assign it a default value?

I thought it would be this, but it doesn't work:

function(nodeBox,str = "hai")
{
    // ...
}

Yeah got to know about this recently. http://es6-features.org/#DefaultParameterValues — Royal Pinto, Oct 13 '15 at 04:40
I would however try and keep the logic in the parameters to a minimum..... — Max, Oct 13 '15 at 06:29

mplungjan · Accepted Answer · 2013-09-03T09:01:20.633

157

If str is null, undefined or 0, this code will set it to "hai"

function(nodeBox, str) {
  str = str || "hai";
.
.
.

If you also need to pass 0, you can use:

function(nodeBox, str) {
  if (typeof str === "undefined" || str === null) { 
    str = "hai"; 
  }
.
.
.

edited Sep 03 '13 at 09:01

answered Jul 16 '11 at 11:46

mplungjan

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@Roayl: This will also work for `false` if that is what you mean. – Felix Kling Jul 16 '11 at 11:50
No default should be true. I mean if i will not pass parametr, it should take true – Royal Pinto Jul 16 '11 at 11:51
OK i will take default as false only. No need set to false. Default it will take as false. – Royal Pinto Jul 16 '11 at 12:04
7

It would be counter intuitive to have a variable you do NOT pass end up as true. – mplungjan Jul 16 '11 at 16:04

sfletche · Answer 2 · 2018-05-14T15:34:37.330

32

ES6 Update - ES6 (ES2015 specification) allows for default parameters

The following will work just fine in an ES6 (ES015) environment...

function(nodeBox, str="hai")
{
  // ...
}

edited May 14 '18 at 15:34

answered Oct 29 '15 at 01:57

sfletche

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score 5 · Answer 3 · answered Apr 12 '13 at 16:18

5

You can also do this with ArgueJS:

function (){
  arguments = __({nodebox: undefined, str: [String: "hai"]})

  // and now on, you can access your arguments by
  //   arguments.nodebox and arguments.str
}

answered Apr 12 '13 at 16:18

zVictor

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How do I set the default value for an optional argument in Javascript?

3 Answers3