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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 string has been padded. If the value is less than the current string's length, the current string is returned as is.
padString Optional
The string to pad the current string with. If this padding string 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 length with the pad string applied from the start.

Example 1

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

Example 2

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

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

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; //truncate if number, or convert non-number to 0;
        padString = String(typeof padString !== 'undefined' ? 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.
Draft Initial definition in ECMAScript 2017.
ECMAScript 2017 (ECMA-262)
The definition of 'String.prototype.padStart' in that specification.
Standard

Browser compatibility

Update compatibility data on GitHub
DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
padStartChrome Full support 57Edge Full support 15Firefox Full support 48IE No support NoOpera Full support 44Safari Full support 10WebView Android Full support 57Chrome Android Full support 57Firefox Android Full support 48Opera Android Full support 43Safari iOS Full support 10Samsung Internet Android Full support 7.0nodejs Full support 8.0.0
Full support 8.0.0
Full support 7.0.0
Disabled
Disabled From version 7.0.0: this feature is behind the --harmony runtime flag.

Legend

Full support  
Full support
No support  
No support
User must explicitly enable this feature.
User must explicitly enable this feature.

See also