JavaScript Regular Expressions
Character classes match a kind of character rather than a specific one.
\d matches any digit, \w any word character.
Square brackets let you define your own set.
Example
javascript
console.log(/\d/.test("abc1"));
console.log(/\d/.test("abc"));The output is true then false.
\d a digit, \D anything but a digit.
\w a letter, digit or underscore; \W the opposite.
\s whitespace; . any character at all.
Syntax
javascript
/\d/ // a digit
/[aeiou]/ // any of theseCapital letters invert the class.
Square brackets match any one of the characters inside.
Example
javascript
console.log(/[aeiou]/.test("sky"));
console.log(/[aeiou]/.test("sun"));The output is false then true.
A dash inside brackets makes a range.
Example
javascript
console.log(/[a-z]/.test("ABC"));
console.log(/[A-Z]/.test("ABC"));
console.log(/[0-9]/.test("42"));[0-9] and \d mean the same thing.
A caret at the start of the brackets inverts the set.
Example
javascript
console.log(/[^0-9]/.test("123"));
console.log(/[^0-9]/.test("12a"));The second is true because of the letter.
A dot matches almost any character.
To match a literal dot, escape it with a backslash.
Example
javascript
console.log(/c.t/.test("cat"));
console.log(/c.t/.test("cut"));
console.log(/file\.txt/.test("file.txt"));Without the backslash, file.txt would also match fileXtxt.
\s covers spaces, tabs and newlines.
Example
javascript
console.log(/\s/.test("no_spaces"));
console.log(/\s/.test("has space"));
console.log("a b".replace(/\s/g, "-"));Replacing whitespace is a common tidying step.
Complete Example
html
<!DOCTYPE html>
<html>
<head>
<title>JavaScript Regex Characters</title>
</head>
<body>
<h1>Regex Characters</h1>
<p id="out"></p>
<script>
const text = "Room 42b";
document.getElementById("out").innerHTML =
"Has a digit: " + /\d/.test(text) +
"<br>Digits found: " + text.match(/\d/g).join("") +
"<br>Has whitespace: " + /\s/.test(text) +
"<br>Vowels: " + text.match(/[aeiou]/gi).join(", ");
</script>
</body>
</html>Run the above example in the Try It Editor.
Try excluding:
Search for /[^0-9]/g and see what comes back.
\d matches a digit and \w a word character.\s matches whitespace.Character classes are the vocabulary of regular expressions.
Most patterns are built from these few symbols.
Escaping the dot is the mistake almost everyone makes once.