Javascript truthy equivalent to not undefined, not null and not empty string?

Question

I found the following legacy Javascript code:

function doSomething(parameter) {
    if (parameter != null && parameter != undefined && parameter != '') {
        ...
    }
}

I wonder if it is equal to check

if(parameter) {
    ...
}

i.e. if it is equal to check if the parameter is truthy. Is there a case when this is not equal?

@RGraham undefined is falsy, what shall your comment say to my question? Am i missing something? — jan
– jan, Commented Dec 13, 2013 at 8:26
these statements are not equivalent for 0, NaN and false. — georg
– georg, Commented Dec 13, 2013 at 8:32
@thg435 only for NaN. false and 0 fall in parameter != '' (see my answer) — Luca Rainone
– Luca Rainone, Commented Dec 13, 2013 at 8:40

Luca Rainone · Accepted Answer · 2013-12-13 08:41:01Z

4

No is not the same. In case of parameter = NaN your IF is true while if(paramater) is evalueted to false.

In fact:

var parameter = NaN;
if (parameter != null && parameter != undefined && parameter != '') {
    console.log("first if");
}
if(parameter) 
     console.log("second if");

just log first if.

In the case of 0 or false the two IF make the same result caused by not strict equality of parameter != ''.

edited Dec 13, 2013 at 8:41

answered Dec 13, 2013 at 8:25

Luca Rainone

16.5k2 gold badges45 silver badges54 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

jan Over a year ago

Thanks for the hint to NaN, now I can martyr myself by deciding whether the orginal coder really intended that or not. ;)

Banana-In-Black · Accepted Answer · 2013-12-13 08:50:28Z

3

Check the link about Converting to Boolean part

http://jibbering.com/faq/notes/type-conversion/

Only NaN, 0, false, null,undefined, '' will be converted to false.

answered Dec 13, 2013 at 8:50

Banana-In-Black

2,5571 gold badge29 silver badges33 bronze badges

Comments

Voonic · Accepted Answer · 2013-12-13 08:23:44Z

1

In javascript there are few values are converted as boolean false else almost all are converted to true

undefined
The empty string ""
null
The number 0
The number NaN
The boolean false

so it better to have

if(!parameter)
{
  // your code
}

answered Dec 13, 2013 at 8:23

Voonic

4,7733 gold badges29 silver badges60 bronze badges

2 Comments

jan Over a year ago

You are right that one often needs !parameter, but in this case with empty string however, you are not right (!'' === true). I don't understand why this answer is upvoted in the context of this question.

Voonic Over a year ago

@jan when you use strict equal to then compares type, i mentioned that comparision result is implicitly converted to boolean false, not the values used to compare.

elclanrs · Accepted Answer · 2013-12-13 08:36:24Z

0

It's all the same as you're using loose comparison != not strict !== so undefined == null, and '' == 0, false == '', etc.

Edit: As pointed out, they're not exactly the same. As a general rule though you'd use either:

if (parameter != null) {

}

Where undefined == null so you check for both. Or:

if (parameter) {

}

Which tests any falsey value such as null, undefined, empty string, zero...

edited Dec 13, 2013 at 8:36

answered Dec 13, 2013 at 8:23

elclanrs

94.2k21 gold badges137 silver badges171 bronze badges

2 Comments

jan Over a year ago

So is this a "yes" and there is no case where the checks don't equal?

elclanrs Over a year ago

There are specific rules. But as a general rule, you usually check in one of the ways I posted above, plus a third way (irrelevant to the question) that tests for existence, with the typeof operator. It depends on the situation.

Collectives™ on Stack Overflow

Javascript truthy equivalent to not undefined, not null and not empty string?

4 Answers 4

1 Comment

Comments

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

1 Comment

Comments

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related