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Quick Tips: String Padding in JS

Nikhil M Warrier
Web Developer and advocate for open standards. Loves JAMstack.
Originally published at nikhil.thedev.id on ・1 min read

Quick Tip #1: String Padding in JavaScript

An example image

Use the padStart() string method with the string length and the string to fill the padding with.

Example:

const text = "Party"
text.padStart(7, "🎉 ") //"🎉 Party"

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Actual Use Case

Suppose you have an array of binary numbers which need not necessarily be in the standard 8-digit format. We want to add "padding" to it so it looks like the 8-digit eyecandy we all know and love.

Here is how to do it:

const binaryNums = [0, 1101, 011010, 1010]
const paddedBinary = []

binaryNums.forEach(num => {
  const str = num.toString(); // convert to string
  const paddedStr = str.padStart(8, "0") // fix the length of string at 8, and add padding with "0"
  paddedBinary.push(Number(paddedStr)
})

// paddedBinary = [00000000, 00001101, 00011010, 00001010]

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See the MDN Docs for more info.

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