padStart(): leading zeros to display

In a few sentences

In brief

Complementary changes the text representation, not the numeric value.

Useful to know

padStart() complements the beginning of a string to a desired length. For example, String(7).padStart(3, "0") returns "007". If the string is already long enough, do not shorten . [1]

This is convenient for numbers in an interface when leading zeros are part of the presentation. For arithmetic, the value can remain a number; the formatted string is a separate result. Do not use the complement as a length validation: four-digit input will not become three-digit just because padStart(3). is submitted

Sources

For further detail and to check the information:

[1] MDN — String.padStart ↗