String.prototype.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

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 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 compatibility

Desktop Mobile
Chrome Edge Firefox Internet Explorer Opera Safari WebView Android Chrome Android Firefox for Android Opera Android Safari on IOS Samsung Internet
padStart
57
15
48
No
44
10
57
57
48
43
10
7.0

See also

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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart