RegEx for whitespaces

What is the regex for whitespace?

Short answer: \s matches one whitespace character: a space, a tab (\t), a line break (\n or \r), a vertical tab (\v) or a form feed (\f). \s+ matches one or more of them in a row, and \S matches any character that is not whitespace. In JavaScript, /\s+/g finds every run of spaces, tabs and line breaks in a string:

const text = "4Geeks   Academy\tMiami\nFlorida";
console.log(text.replace(/\s+/g, " ")); // "4Geeks Academy Miami Florida"

A literal space in a pattern, as in / /, matches only the space bar character. It does not match tabs or line breaks.

\s finds whitespace, \s+ groups it into runs and \S matches everything else. With these three you can check, clean and split almost any text.

Whitespace regex patterns at a glance

Check if a string contains whitespace

test() returns true or false in JavaScript, and re.search() returns a match or None in Python:

const hasWhitespace = (str) => /\s/.test(str);
 
console.log(hasWhitespace("4Geeks Academy")); // true
console.log(hasWhitespace("4GeeksAcademy"));  // false
console.log(hasWhitespace("4Geeks\tAcademy")); // true, a tab counts

import re
 
def has_whitespace(text):
    return re.search(r"\s", text) is not None
 
print(has_whitespace("4Geeks Academy"))  # True
print(has_whitespace("4GeeksAcademy"))   # False

To check a URL before you use it, the same pattern catches the space that breaks it:

const url = "https://4geeks.com/how to";
if (/\s/.test(url)) {
  console.log("Whitespace found in the URL");
}

Replace or remove whitespace

Use replace() with the g flag in JavaScript, or re.sub() in Python, which replaces every match by default:

const messy = "  Learn   to\tcode \n with   AI  ";
 
console.log(messy.replace(/\s+/g, ""));        // "LearntocodewithAI"
console.log(messy.replace(/\s+/g, " ").trim()); // "Learn to code with AI"
console.log(messy.replace(/^\s+|\s+$/g, ""));   // same as messy.trim()

import re
 
messy = "  Learn   to\tcode \n with   AI  "
 
print(re.sub(r"\s+", "", messy))          # LearntocodewithAI
print(re.sub(r"\s+", " ", messy).strip())  # Learn to code with AI
print(" ".join(messy.split()))            # same result, without regex

Without the g flag, JavaScript only replaces the first match: "a b c".replace(/\s+/, "") returns "ab c".

Split a string on whitespace

Splitting on a single space leaves empty items when there are double spaces. Split on \s+ and trim first:

const line = "  red   green\tblue ";
 
console.log(line.split(" "));            // ["", "", "red", "", "", "green\tblue", ""]
console.log(line.trim().split(/\s+/));   // ["red", "green", "blue"]
console.log(line.match(/\S+/g));         // ["red", "green", "blue"]

In Python, split() with no arguments already splits on any run of whitespace and ignores the ends: " red green\tblue ".split() returns ['red', 'green', 'blue'].

Use whitespace regex with AI

An AI assistant such as ChatGPT, Claude or GitHub Copilot writes and explains regex quickly, but it can miss cases you did not mention. Give it real input, the output you expect and the language you use. These three prompts are ready to copy.

1. Write the pattern for your case

I need a regex in [JavaScript / Python] that [collapses repeated spaces / removes spaces but keeps line breaks / rejects usernames with whitespace].
Input: [paste 3 real examples]
Expected output: [paste what each one should become]
Explain each part of the pattern and give me the code.

2. Debug a pattern that does not match

This regex does not work as I expect in [language]:
[paste the line, e.g. new RegExp("\s+")]
Input: [paste the text]  Result: [paste what you got]
Explain why and give me the fix.

3. Test the edge cases

Write tests for this whitespace regex: [paste it]
Include tabs, Windows line breaks (\r\n), non-breaking spaces ( ), empty strings and leading and trailing spaces.

Run the answer against your own examples before you use it. Online testers such as regex101 show what each part of the pattern matches.

\s in JavaScript, Python and Java

\s means the same thing everywhere for spaces, tabs and line breaks, but each language writes it differently and treats Unicode spaces differently:

In JavaScript, \s also matches the byte order mark () that some files start with. Python's \s does not.

Match spaces and tabs but not line breaks

\s includes \n and \r, so /\s+/g joins all your lines into one. To clean each line and keep the line breaks, use a character class:

const text = "name:   Ana \t\nrole:\t\tdev";
 
console.log(text.replace(/[ \t]+/g, " "));
// "name: Ana \nrole: dev"

[^\S\r\n] is a stricter version: any whitespace except line breaks, including non-breaking spaces.

Remove non-breaking spaces from copied text

Text copied from web pages, PDFs or Word often contains non-breaking spaces ( ). They look like normal spaces, but " " does not match them. \s does, in JavaScript and in Python:

const copied = "Total: 250";
console.log(copied.split(" "));            // ["Total: 250"]
console.log(copied.replace(/\s/g, " "));   // "Total: 250"

The zero-width space (​) is not whitespace for regex, so remove it explicitly with /​/g.

Validate input with no whitespace

Anchor \S+ to the start and end of the string to reject any value that contains a space, a tab or a line break:

const isValidUsername = (name) => /^\S+$/.test(name);
 
console.log(isValidUsername("ana_dev"));  // true
console.log(isValidUsername("ana dev"));  // false
console.log(isValidUsername(""));         // false, + needs one character

import re
 
print(bool(re.fullmatch(r"\S+", "ana_dev")))  # True
print(bool(re.fullmatch(r"\S+", "ana dev")))  # False

Common errors with whitespace regex

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