Understanding JavaScript Truthy and Falsy

Question

Can someone please explain JavaScript Truthy and Falsy, using the below sample data. I have read other threads but still confused.

var a = 0;  var a = 10 == 5;  var a = 1;   var a = -1; 

From my understanding, I believe that var a = 1; is the only truthy and the rest are falsy - is this correct?

Answer 1

From my understanding, I believe that var a = 1; is the only truthy and the rest are falsy’s - is this correct?

No.

1. var a = 0;

   Number zero is falsy. However, note that the string zero "0" is truthy.

2. var a = 10 == 5;

   This is same as var a = (10 == 5);, so this is falsy.

3. var a = 1;

   var a = -1;

   Any non-zero number including negative numbers is truthy.

Quoting from MDN

In JavaScript, a truthy value is a value that translates to true when evaluated in a Boolean context. All values are truthy unless they are defined as falsy (i.e., except for false, 0, "", null, undefined, and NaN).

List of falsy values in JavaScript:^{From MDN}

1. false
2. null
3. undefined
4. 0
5. NaN
6. '', "", ``(Empty template string)
7. document.all
8. 0n: BigInt
9. -0

Answer 2

There's a simple way to check, which you can use now and forever:

function truthyOrFalsy(a) {     return a ? "truthy" : "falsy"; } 

To wit:

> truthyOrFalsy(0) "falsy" > truthyOrFalsy(10 == 5) "falsy" > truthyOrFalsy(1) "truthy" > truthyOrFalsy(-1) "truthy" 

Also see a list of all falsey values in JavaScript.