JavaScript String trim() Method

What You’ll Learn

String.prototype.trim() returns a new string with whitespace removed from both ends (same API as MDN String.prototype.trim()). Learn what counts as whitespace, how it differs from trimStart() / trimEnd(), cleaning form input, five examples, and try-it labs.

Introduction

User input and pasted text often include accidental spaces, tabs, or newlines at the edges. trim() strips that padding from both ends so comparisons and validation stay reliable.

Middle spaces stay put — "Hello world" remains two words. For only the start or only the end, use trimStart() or trimEnd().

This page is part of JavaScript String Methods. Related topics include toLowerCase() and padStart().

Understanding the trim() Method

str.trim() builds a new string with leading and trailing whitespace removed. Whitespace means white space characters plus line terminators (spaces, tabs, newlines, and similar).

• Returns a new string — the original is unchanged.
• Takes no parameters.
• Does not remove spaces between words.
• Still returns a new string when there was nothing to trim.

📝 Syntax

General form of String.prototype.trim:

str.trim()

Parameters

None.

Return value

A new string representing str with whitespace stripped from both its beginning and end.

Exceptions

None for normal string values.

Common patterns

"   Hello world!   ".trim();  // "Hello world!"
"   foo  ".trim();            // "foo"
"\t\n hi \r".trim();          // "hi"
"no-spaces".trim();           // "no-spaces"
"  a  b  ".trim();            // "a  b" (middle spaces kept)

Examples Gallery

Examples follow MDN String.trim() patterns plus everyday beginner tips. Use View Output or Try It Yourself for each case.

const greeting = "   Hello world!   ";

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

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

   Hello world!   
Hello world!

const str = "   foo  ";
console.log(str.trim());
// 'foo'

foo

const messy = "\t\n hi \r";

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

console.log("no-spaces".trim());
// "no-spaces"

"\t\n hi \r"
"hi"
no-spaces

const padded = "  hi  ";

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

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

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

"hi"
"hi  "
"  hi"

function cleanUsername(raw) {
  return raw.trim().toLowerCase();
}

const typed = "  Ada  ";
const cleaned = cleanUsername(typed);

console.log(cleaned);                 // "ada"
console.log(typed.trim() === "");     // false
console.log("   ".trim() === "");     // true — empty after trim
console.log("  a  b  ".trim());       // "a  b"

ada
false
true
a  b

🎯 Common Use Cases

• Form fields — names, emails, search boxes before validate/save.
• Empty checks — value.trim() === "" catches space-only input.
• Normalize before compare — often chained with toLowerCase().
• Not for mid-string spaces — use replace / regex to collapse them.
• Not one-sided — use trimStart / trimEnd when needed.

📝 Notes

• Always returns a new string — assign it if you need the result.
• Does not collapse repeated spaces inside the text.
• Whitespace includes more than " " — tabs and line breaks count too.
• Safe to call when there is nothing to trim.
• Older docs may mention trimLeft / trimRight — prefer trimStart / trimEnd.

💡 Best Practices