How to check for falsey string value when concatenating?

Question

In the following examples both ex1 & ex2 variables will render an empty string with a space and not a falsy value. Whereas ex3 will be falsy and render the right side of the || operator. How can I test for empty string in the first two examples without doing an if statement?

let var1 = '';
let var2 = '';
let ex1 = `${var1} ${var2}` || "Is Falsy";
let ex2 = var1 + ' ' + var2 || "Is Falsy";
let ex3 = var1 || "Is Falsy";

What have you tried so far to solve this on your own? If you already know that an empty string is "falsy" and that `||` would help with that... What would be the next step? — Andreas, Oct 05 '21 at 12:23
I think you might want to use [`.trim()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim) before checking. — Rojo, Oct 05 '21 at 12:53

score 1 · Accepted Answer · answered Oct 05 '21 at 12:41

1

i think this will work for you :

let ex2 = var1 || var2 || "Is Falsy";

answered Oct 05 '21 at 12:41

Said Taher

51
3

@coolps811 Why is this the accepted answer? `ex2` will be the first non-empty string. If both are not empty the result will be different to `ex2` (or `ex1`) in your question. – Andreas Oct 06 '21 at 07:54

score 0 · Answer 2 · answered Oct 05 '21 at 12:23

0

Are ternary operators acceptable?

let ex1 = var1 && var2 ? `${var1} ${var2}` : "Is Falsy";

answered Oct 05 '21 at 12:23

Jamiec

133,658
13
134
193

score 0 · Answer 3 · answered Oct 05 '21 at 12:23

If you are okay with using conditional operators, this can be done with the help of trim() :

let var1 = '';
let var2 = '';
let ex1 = (`${var1} ${var2}`).trim()/length > 0 ? `${var1} ${var2}` : "Is Falsy";
let ex2 = (var1 + ' ' + var2).trim().length > 0 ? var1 + ' ' + var2 : "Is Falsy";
let ex3 = var1 || "Is Falsy";
console.log(ex1);
console.log(ex2);
console.log(ex3);

score 0 · Answer 4 · answered Oct 05 '21 at 12:33

Use ternary operators:

let var1 = '';
let var2 = '';
let ex1 = (`${var1} ${var2}`).trim().length > 0 ? `${var1} ${var2}` : "Is Falsy";
let ex2 = (var1 + ' ' + var2).trim().length > 0 ? var1 + ' ' + var2 : "Is Falsy";
let ex3 = var1.trim().length > 0 ? var1 : "Is Falsy";

score -1 · Answer 5 · answered Oct 05 '21 at 12:27

-1

You can try this typing method:

const str = "not empty"

console.log(!str); // will be false, to check if a string is empty
console.log(!!str); // will be true, to check if a string is not empty

answered Oct 05 '21 at 12:27

Tomer Alony

34
2

How to check for falsey string value when concatenating?

5 Answers5