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string.padStart

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

Syntax

str.padStart(targetLength [, padString])

Parameters

targetLength
The length of the resulting string once the current str has been padded. If the value is less than 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 " " (U+0020 'SPACE').

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));
// expected output: "00123"

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
padStart 57 15 48 No 44 10
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
padStart 57 57 48 43 10 7.0
Server
Node.js
padStart 8.0.0
8.0.0
7.0.0
Disabled
Disabled From version 7.0.0: this feature is behind the --harmony runtime flag.

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart