JavaScript String trimStart() Method

What You’ll Learn

String.prototype.trimStart() returns a new string with whitespace removed from the start only (same API as MDN String.prototype.trimStart()). Learn the trimLeft alias, how it differs from trim() / trimEnd(), five examples, and try-it labs.

Introduction

Sometimes you need to drop leading spaces, tabs, or indentation but keep trailing padding. That is exactly what trimStart() does — clean the left side only.

After trim() was standardized, engines also had a non-standard trimLeft(). The standard name is trimStart() (to match padStart()), and trimLeft remains as an alias of the same function for compatibility.

This page is part of JavaScript String Methods. Related topics include trim() and trimEnd().

Understanding the trimStart() Method

str.trimStart() builds a new string with leading whitespace removed. Trailing whitespace and middle spaces stay unchanged.

• Returns a new string — the original is unchanged.
• Takes no parameters.
• Only the start (left side) is cleaned.
• trimLeft is the same function (alias).

📝 Syntax

General form of String.prototype.trimStart:

str.trimStart()
str.trimLeft()  // alias — same function

Parameters

None.

Return value

A new string representing str stripped of whitespace from its beginning. If there is no leading whitespace, a new string is still returned (essentially a copy).

Exceptions

None for normal string values.

Aliasing

trimLeft and trimStart refer to the exact same function object. In some engines, String.prototype.trimLeft.name === "trimStart".

Common patterns

"   Hello world!   ".trimStart();  // "Hello world!   "
"   foo  ".trimStart();            // "foo  "
"\t hi \n".trimStart();            // "hi \n"
"no-spaces".trimStart();           // "no-spaces"

Examples Gallery

Examples follow MDN String.trimStart() patterns. Use View Output or Try It Yourself for each case.

const greeting = "   Hello world!   ";

console.log(greeting);
// Expected output: "   Hello world!   ";

console.log(greeting.trimStart());
// Expected output: "Hello world!   ";

   Hello world!   
Hello world!   

let str = "   foo  ";

console.log(str.length); // 8

str = str.trimStart();
console.log(str.length); // 5
console.log(str);        // 'foo  '

8
5
foo  

const padded = "  hi  ";

console.log(padded.trimStart() === padded.trimLeft());
// true

console.log(String.prototype.trimStart === String.prototype.trimLeft);
// true

console.log(String.prototype.trimLeft.name);
// "trimStart" (in many engines)

true
true
trimStart

const padded = "  hi  ";

console.log(JSON.stringify(padded.trimStart()));
// "hi  "

console.log(JSON.stringify(padded.trim()));
// "hi"

console.log(JSON.stringify(padded.trimEnd()));
// "  hi"

"hi  "
"hi"
"  hi"

function deindent(line) {
  return line.trimStart();
}

const padded = "    value  ";
const cleaned = deindent(padded);

console.log(JSON.stringify(cleaned));
// "value  "

console.log(cleaned.startsWith(" ")); // false — leading gone
console.log(cleaned.endsWith("  "));  // true — trailing kept

"value  "
false
true

🎯 Common Use Cases

• Remove indentation — strip leading spaces/tabs while keeping end padding.
• Fixed-width fields — drop left pad, keep right alignment spaces.
• Pasted text cleanup — remove accidental leading whitespace only.
• Not for form fields — usually prefer trim() (both ends).
• Not mid-string spaces — use replace / regex for those.

📝 Notes

• Always returns a new string — assign it if you need the result.
• Trailing whitespace is intentionally kept.
• trimLeft is an alias — prefer trimStart in new code.
• Does not change spaces in the middle of the string.
• Named to mirror padStart() after standardization.

💡 Best Practices