String.prototype.padStart()

The padStart() method of String values pads this string with another string (multiple times, if needed) until the resulting string reaches the given length. The padding is applied from the start of this string.

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Syntax

padStart(targetLength)
padStart(targetLength, padString)

Parameters

targetLength: The length of the resulting string once the current str has been padded. If the value is less than or equal to str.length, then str is returned as-is.
padString Optional: The string to pad the current str with. If padString is too long to stay within the targetLength, it will be truncated from the end. The default value is the unicode "space" character (U+0020).

Return value

A String of the specified targetLength with padString applied from the start.

Examples

Basic examples

"abc".padStart(10); // "       abc"
"abc".padStart(10, "foo"); // "foofoofabc"
"abc".padStart(6, "123465"); // "123abc"
"abc".padStart(8, "0"); // "00000abc"
"abc".padStart(1); // "abc"

Fixed width string number conversion

// JavaScript version of: (unsigned)
// printf "%0*d" width num
function leftFillNum(num, targetLength) {
  return num.toString().padStart(targetLength, "0");
}

const num = 123;
console.log(leftFillNum(num, 5)); // "00123"

Specifications

Specification
ECMAScript Language Specification # sec-string.prototype.padstart

Browser compatibility

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Opera	Safari	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet	WebView Android	Deno	Node.js
`padStart`	57	15	48	44	10	57	48	43	10	7.0	57	1.0	8.0.0

Docs

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