The JavaScript function `Math.abs()`

is a built-in function that returns the absolute value of a number. The absolute value of a number is its distance from zero, regardless of whether the number is positive or negative.

Here is an example of how to use the `Math.abs()`

function:

```
let num1 = -5;
let num2 = 5;
console.log(Math.abs(num1)); // Output: 5
console.log(Math.abs(num2)); // Output: 5
```

In the above example, `num1`

is assigned the value of -5 and `num2`

is assigned the value of 5. When the `Math.abs()`

function is called on these variables, it returns the absolute value of each number, which is 5 in both cases.

You can also use the `Math.abs()`

function on decimal numbers:

```
let num3 = -3.14;
let num4 = 3.14;
console.log(Math.abs(num3)); // Output: 3.14
console.log(Math.abs(num4)); // Output: 3.14
```

As you can see, the `Math.abs()`

function works the same way on decimal numbers as it does on whole numbers.

It is also worth noting that the `Math.abs()`

function does not modify the original variable and returns a new value.

The `Math.abs()`

function can be useful in a variety of situations, such as when you need to determine the distance between two points on a coordinate plane or when you need to calculate the magnitude of a vector.

In short, the JavaScript function `Math.abs()`

returns the absolute value of a number, regardless of whether it is positive or negative. It can be used on both whole numbers and decimal numbers and is a useful tool for a variety of mathematical calculations.