JS RegExp Metachars

JavaScript RegExp Metacharacters

In Regular Expressions, Metacharacters are characters with a special structural or structural meaning. They are the engine of regular expressions, allowing you to define wildcards, alternatives, and more.

Essential Metacharacters

(Note: Characters like ^, $, *, +, and ? are also metacharacters, but we will cover them in the Assertions and Quantifiers chapters!)

1. The Dot Wildcard (.)

The dot . acts as a wildcard. It will match any single character except for line breaks.

let text = "That's hot! The hat is on the mat.";

// Match 'h', followed by ANY character, followed by 't'
let result = text.match(/h.t/g);
console.log(result); // ["hot", "hat"]

2. Alternation (|)

The pipe character | acts like a boolean OR. It allows your regular expression to match one pattern or another pattern.

let text = "I have a red car, a green bike, and a blue boat.";

// Find "red", OR "green", OR "blue"
let result = text.match(/red|green|blue/g);
console.log(result); // ["red", "green", "blue"]

3. Escaping Characters (\)

Because characters like ., |, ?, and * have special powers in regular expressions, what happens if you actually want to search for a literal question mark or a literal period in your text?

You must escape the character by placing a backslash \ directly in front of it.

let text = "Hello. How are you?";

// BAD: This searches for ANY character (wildcard)
console.log(text.match(/./g)); 
// GOOD: The backslash escapes the dot, so it searches for a literal period
let period = text.match(/./g);
console.log(period); // ["."]
// Escaping a question mark
let question = text.match(/?/g);
console.log(question); // ["?"]