The String trimStart() method

trimStart() returns a new string with the white space removed from the start of the original string. White space at the end is left in place:

'Testing'.trimStart() //'Testing'
' Testing'.trimStart() //'Testing'
' Testing '.trimStart() //'Testing '
'Testing '.trimStart() //'Testing'

It removes spaces, tabs, newlines and any other Unicode whitespace character.

A string made entirely of white space becomes an empty string. A string with no leading white space comes back unchanged.

The original string is untouched

Strings are immutable in JavaScript, so trimStart() returns a new string:

const city = '   Milan'
const trimmed = city.trimStart()

city //'   Milan'
trimmed //'Milan'

If you call the method without using its return value, nothing visible happens. That’s the mistake I see most often. Remember to assign the result.

trimStart() vs trim() vs trimEnd()

The three trimming methods differ in which end they clean:

• trim() cleans both ends
• trimStart() cleans only the beginning
• trimEnd() cleans only the end

Most of the time trim() is what you want, for example when cleaning up values typed into a form. Reach for trimStart() when white space at the end matters and you only want to fix the beginning.

A real-world case

Say you’re parsing indented lines from a config file, and you want the content without the indentation:

const line = '    port: 3000'

line.trimStart() //'port: 3000'

The leading spaces are gone, and anything at the end of the line survives.

What about other characters?

Here’s a pitfall: trimStart() only handles white space. It won’t remove other leading characters, like the zeros in '00042'. For those, use a regular expression:

'00042'.replace(/^0+/, '') //'42'

You might also bump into trimLeft() in older codebases. It’s a legacy alias of trimStart(), kept for compatibility. Write trimStart() in new code, it’s the standard name.