How to define a variable in JavaScript that is empty but gives true for a if condition

Question

var a = '';
if (a) {
  console.log("True Value");
} else {
  console.log("False Value");
}

The above code logs "False Value" for obvious reasons, I want to set variable 'a' to a empty value such that it return true when used with if and logs "True Value".

Setting 'a' to empty object/array works fine but, I also want to do comparison between two variables but that is not possible with objects as they are compared by reference and not value.

Also I can not change the if else condition as it handles many cases other than this.

actually the code in which I have to use this concept has many cases and I cant change the code just for this specific case. — Utkarsh Prakash, Mar 21 '17 at 08:48
possible duplicate http://stackoverflow.com/questions/154059/how-do-you-check-for-an-empty-string-in-javascript — Kapila Perera, Mar 21 '17 at 08:49
Possible duplicate of [How do you check for an empty string in JavaScript?](http://stackoverflow.com/questions/154059/how-do-you-check-for-an-empty-string-in-javascript) — Kapila Perera, Mar 21 '17 at 08:50
_I can not change the if else condition_ You want us to help change your code, **without** actually changing anything? — George, Mar 21 '17 at 09:02
I think the rule is we can only change the assignment of `a`. The rest of the code is off limits. I am not sure what "empty" means though. — John Wu, Mar 21 '17 at 09:12

synthet1c · Answer 1 · 2017-03-21T08:50:38.510

0

I'm not sure you worded the question correctly. this will check if the value is not null or undefined therefore any other falsey value will evaluate to true in the if statement. eg. [], 0 and false will pass

var a  = '';
if(a != null){
  console.log("True Value");
}else{
  console.log("False Value" );
}

edited Mar 21 '17 at 08:50

answered Mar 21 '17 at 08:44

synthet1c

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score 0 · Answer 2 · answered Mar 21 '17 at 08:57

0

Probably this?

// allow empty values inside, but false if undefined
if (typeof a !== 'undefined') {
  // true
}

answered Mar 21 '17 at 08:57

Alex K

6,737
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Gaurav Chaudhary · Answer 3 · 2017-03-21T09:37:12.640

0

You need to change your if else condition or assignment of var 'a' because we can't change javascript behavior. It will always consider empty string as falsy value!

I hope it works for you

var a = '';
var a = (a) ? false : true;
if (a) {
  console.log("True Value");
} else {
  console.log("False Value");
}

edited Mar 21 '17 at 09:37

answered Mar 21 '17 at 08:58

Gaurav Chaudhary

1,491
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John Wu · Answer 4 · 2017-03-21T09:20:10.597

0

OP, I infer your requirements to be:

Cannot change any Javascript code, only the contents of a
The code snip must output "True Value".
Must be a value type.
Must be "empty," whatever that means.

Anyway how about this:

var a = '\0';  //Null
if (a) {
  console.log("True Value");
} else {
  console.log("False Value");
}

alert("See? It's empty. No space.>>>" + a + "<<<");

edited Mar 21 '17 at 09:20

answered Mar 21 '17 at 09:06

John Wu

50,556
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How to define a variable in JavaScript that is empty but gives true for a if condition

4 Answers4