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.
The source for this interactive example is stored in a GitHub repository. If you'd like to contribute to the interactive examples project, please clone https://github.com/mdn/interactive-examples and send us a pull request.
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 "
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, targetLength) { return num.toString().padStart(targetLength, 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(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
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Update compatibility data on GitHub
Desktop | Mobile | Server | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
padStart | Chrome Full support 57 | Edge Full support 15 | Firefox Full support 48 | IE No support No | Opera Full support 44 | Safari Full support 10 | WebView Android Full support 57 | Chrome Android Full support 57 | Firefox Android Full support 48 | Opera Android Full support 43 | Safari iOS Full support 10 | Samsung Internet Android Full support 7.0 | nodejs
Full support
8.0.0
|
Legend
- Full support
- Full support
- No support
- No support
- User must explicitly enable this feature.
- User must explicitly enable this feature.