How Can I Add Leading Zeros to Numbers in JavaScript?

Prepending Leading Zeros to Numbers in JavaScript

Is there a way to add leading zeros to numbers in order to obtain a string with a consistent length? For instance, the number 5 should be converted to "05" if two digits are specified.

Solution:

To add leading zeros, you need to convert the number into a string because numbers don't recognize leading zeros. Here's one way to achieve this:

function pad(num, size) {
    num = num.toString();
    while (num.length < size) num = "0" + num;
    return num;
}

For example, if you want to add two leading zeros to the number 5:

pad(5, 2); // returns "05"

However, this function assumes that you'll never need more than 10 leading zeros. If you anticipate larger values, you can use a different approach:

function pad(num, size) {
    var s = "000000000" + num;
    return s.substr(s.length - size);
}

For example:

pad(5, 6); // returns "000005"

Note that if you need to handle negative numbers, you'll need to remove and re-add the negative sign after padding.

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