javascript if(-1) {...statement...} evaluates to true

Question

I have a condition where 0 or more is valid and negative is invalid. When I write code accordingly in JavaScript/TypeScript, to my surprise it's not working the way I expected it to.

The code is as follows.

if (-1) {
  console.log("truthy")
} else {
  console.log("falsy")
}

And this prints the following in console.

truthy

It should have be falsy, right?

Any help, helping me understand this behavior. What am I missing?

Thanks

`-1` is a truthy value. The only falsy values are `0`, `""`, `false`, `undefined`, `null` and `NaN`. *Everything else is truthy*. — CRice, Jul 19 '18 at 16:37

score 7 · Accepted Answer · answered Jul 19 '18 at 16:37

7

There are six falsy values in JavaScript:

false
0
NaN
undefined
''
null

All other values are truthy.

answered Jul 19 '18 at 16:37

pete

24,141
4
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51

score 0 · Answer 2 · answered Jul 19 '18 at 16:38

0

In Javascript, 0 is always evaluated to falsy, and any non-zero number is truthy.

answered Jul 19 '18 at 16:38

Ruben Krueger

51
2
4

score 0 · Answer 3 · answered Jul 19 '18 at 16:39

0

In javascript non-zero numbers evaluate to true while zero evaluates to false. Heres a nice webpage that goes deep on the boolean evaluations of many different values in javascript: https://www.sitepoint.com/javascript-truthy-falsy/

answered Jul 19 '18 at 16:39

Zackary Jones

371
1
9

javascript if(-1) {...statement...} evaluates to true

3 Answers3