# Check if a number is an integer in JavaScript

July 11, 2022 ‐ **1 min read**

In certain cases you need to check whether the number that is passed as an argument or so is an integer.

For such a use-case we use the method `Number.isInteger()`

. Which returns `true`

if the number is an integer and `false`

otherwise.

```
Number.isInteger(42);
//=> true
```

Seems pretty straight forward but there are a couple gotchas to be aware of.

This one is probably as expected but integers as a string evaluate to `false`

. If you are expecting an integer from a form field you should parse it first to an integer.

```
Number.isInteger('42');
//=> false
```

Floating-point looking values which represent an integer evaluate to `true`

:

```
Number.isInteger(42.0);
//=> true
```

The same as above holds up when the precision limit of floats is exceeded, therefore the following evaluates to `true`

:

```
Number.isInteger(42.000000000000001);
//=> true
```

But with one less zero it evaluates to `false`

:

```
Number.isInteger(42.00000000000001);
//=> false
```