Sometimes, we may want to format our numbers by pretending zeroes before it until it matches a given length.

In this article, we’ll look at how to format numbers by padding a number with leading zeroes until it meets a given length.

### Number.prototype.toLocaleString

One way to pad a number with leading zeroes is to use the `toLocaleString`

method.

It lets us pad a number with leading zeroes until it reaches a minimum length.

For instance, we can write:

```
const formattedNumber = (2).toLocaleString('en-US', {
minimumIntegerDigits: 2,
useGrouping: false
})
console.log(formattedNumber)
```

To pad the number 2 with leading zeroes until it’s 2 digits long.

`minimumIntegerDigits`

is set to 2 so that the returned number string will be at least 2 characters long.

`useGrouping`

set to `false`

removes any digit grouping separator for the given locale.

Therefore, `formattedNumber`

is `'02'`

.

### Write Our Own Function

We can also write our own function to pad a number string until it meets the given length.

For instance, we can write:

```
function leftPad(number, targetLength) {
let output = number.toString();
while (output.length < targetLength) {
output = '0' + output;
}
return output;
}
const formattedNumber = leftPad(2, 2)
console.log(formattedNumber)
```

We create the `leftPad`

function that takes the `number`

to format and the `targetLength`

to pad to as arguments.

We convert the `number`

to a string with the `toString`

method and assign it to `output`

.

Then we use a `while`

loop to prepend the `output`

with zeroes until the `targetLength`

is met.

Then we return the `output`

string.

So when we call `leftPad`

with 2 and 2, we get `'02'`

.

### String.prototype.padStart

Another way to pad a number string with zeroes until a given length is to use the string `padStart`

method.

For instance, we can write:

```
const formattedNumber = (2).toString().padStart(2, "0");
console.log(formattedNumber)
```

We call `toString`

on 2 to convert it to a string.

Then we call `padStart`

on it with the length that we want to pad to and the character to pad the string with.

`padStart`

prepends the string with the characters in the 2nd argument repeatedly until the length in the first argument is met.

Therefore, `formattedNumber`

is the same as the other examples.

### Conclusion

We can format numbers with leading zeroes until it meets a given length with JavaScript with a few simple methods or operations.