How to Format Numbers by Prepending a 0 to Single-Digit Numbers in JavaScript?

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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.