Baseline Widely available
The padStart() method of String values pads this string with a given string (repeated and/or truncated, if needed) so that the resulting string has a given length. The padding is applied from the start of this 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
The length of the resulting string once the current str has been padded. If the value is less than or equal to str.length, then str is returned as-is.
padString Optional
The string to pad the current str with. If padString is too long to stay within targetLength, it will be truncated from the end. The default value is the space character (U+0020).
A String of the specified targetLength with padString applied at the start.
"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"
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