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This feature is well established and works across many devices and browser versions. Its been available across browsers since 2017 4.
padStart() String , ( ) .
.
const str1 = "5";
console.log(str1.padStart(2, "0"));
// Expected output: "05"
const fullNumber = "2034399002125581";
const last4Digits = fullNumber.slice(-4);
const maskedNumber = last4Digits.padStart(fullNumber.length, "*");
console.log(maskedNumber);
// Expected output: "************5581"
padStart(targetLength)
padStart(targetLength, padString)
targetLength str .
str.length ,
str .
padString Optional str .
padString targetLength ,
.
"space" (U+0020).
targetLength String, padString .
"abc".padStart(10); // " abc"
"abc".padStart(10, "foo"); // "foofoofabc"
"abc".padStart(6, "123465"); // "123abc"
"abc".padStart(8, "0"); // "00000abc"
"abc".padStart(1); // "abc"
// 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)); // "00123"
| Specification |
|---|
| ECMAScript 2027 LanguageSpecification # sec-string.prototype.padstart |
This page was last modified on 2025 2 11 by MDN contributors.
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