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The padStart() method pads the current string with another string (repeated, if needed) so that the resulting string reaches the given length. The padding is applied from the start (left) of the current string.

Syntax

str.padStart(targetLength [, padString])

Parameters

targetLength
The length of the resulting string once the current string has been padded. If the value is lower than the current string's length, the current string will be returned as is.
padString Optional
The string to pad the current string with. If this string is too long to stay within the target length, it will be truncated and the left-most part will be applied. The default value for this parameter is " " (U+0020).

Return value

A String of the specified length with the pad string applied from the start.

Examples

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

Polyfill

Running the following code before any other code will create String.prototype.padStart() if it's not natively available.

// https://github.com/uxitten/polyfill/blob/master/string.polyfill.js
// https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/padStart
if (!String.prototype.padStart) {
    String.prototype.padStart = function padStart(targetLength,padString) {
        targetLength = targetLength>>0; //floor if number or convert non-number to 0;
        padString = String(padString || ' ');
        if (this.length > targetLength) {
            return String(this);
        }
        else {
            targetLength = targetLength-this.length;
            if (targetLength > padString.length) {
                padString += padString.repeat(targetLength/padString.length); //append to original to ensure we are longer than needed
            }
            return padString.slice(0,targetLength) + String(this);
        }
    };
}

Specifications

Specification Status Comment
ECMAScript Latest Draft (ECMA-262)
The definition of 'String.prototype.padStart' in that specification.
Living Standard Initial definition in ECMAScript 2017.
ECMAScript 2017 (ECMA-262)
The definition of 'String.prototype.padStart' in that specification.
Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support571548 No4410
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support ?57 Yes48 No ?10

See also

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