String.prototype.padStart(targetLength, padString?) returns a new string padded at the start until it reaches targetLength. Default filler is a space. It never mutates the original.
Pass the required arguments shown below. Check return values and browser support before you rely on the result.
Call string.padStart. Start with this line.
str.padStart(targetLength, padString?)| Call | What it does |
|---|---|
str.padStart(targetLength, padString?) | Primary signature. |
string.padStart(...) | Call with the arguments your case needs. |
Built into JavaScript. Call padStart(...) on a string (or String instance) — no import required.
str.padStart(targetLength, padString?)| Parameter | Description |
|---|---|
| targetLength | Required. Desired final .length (UTF-16 units) |
| padString | Optional. Filler; default " "; truncated if too long |
| Return Value | Description |
|---|---|
| * | The value returned by string.padStart(). |
Pad on the left with "0" or the default space.
console.log("5".padStart(3, "0")); // "005"
console.log("200".padStart(5)); // " 200""5" has length 1; target is 3 → need 2 chars."0" characters make "005".padString pads "200" with two spaces on the left.A short filler repeats; a long filler is cut to fit exactly.
console.log("abc".padStart(10, "foo")); // "foofoofabc"
console.log("abc".padStart(6, "123456")); // "123abc"
console.log("abc".padStart(2, ".")); // "abc""foo" is tiled until seven chars are needed → "foofoof"."123456" are kept → "123abc".2 is already less than length 3 → "abc".result.length === targetLength.padStart() vs padEnd()Left pad for zeros; right pad for labels.
console.log(String(9).padStart(2, "0") + ":" + String(5).padStart(2, "0")); // "09:05"
console.log("5".padStart(3, "0")); // "005"
console.log("5".padEnd(3, "0")); // "500"String(9) becomes "9", then pads to "09".2 → "09:05".padStart → "005"; padEnd → "500".padStart; right-side fill → padEnd.String.prototype.padStart() is part of ES2017 and is Baseline Widely available across modern browsers.
Supported in Chrome 57+, Firefox 48+, Safari 10+, Edge 15+, and Node.js 8+. Not available in Internet Explorer without a polyfill.
Bottom line: Safe for modern web apps and current Node LTS releases. Feature-detect with if ("padStart" in String.prototype) or use a small polyfill for very old targets.
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