Regex metacharacters dot star plus question mark explained

Metacharacters Are Not Literals

Most characters in a regex match themselves. A handful have special meaning — these are metacharacters. The most-used four are . * + ?.

• . — matches any single character except a newline
• * — zero or more of the preceding element
• + — one or more of the preceding element
• ? — zero or one of the preceding element (makes it optional)

Examples

/c.t/.test('cat')  // true  — dot matches 'a'
/c.t/.test('ct')   // false — dot requires exactly one char
/ca*t/.test('ct')  // true  — zero 'a's is valid
/ca+t/.test('ct')  // false — needs at least one 'a'
/colou?r/.test('color')  // true
/colou?r/.test('colour') // true

Escaping Metacharacters

To match a literal dot, star, or plus, escape it with a backslash.

/3\.14/.test('3.14')  // true  — escaped dot matches literal dot
/3\.14/.test('3X14')  // false

Greedy by default: * and + consume as many characters as possible while still allowing the overall pattern to match. This matters when patterns overlap — covered in the quantifiers module.

Knowing when to escape is critical. Characters outside a character class that need escaping include: . * + ? ( ) [ ] { } ^ $ | \. Inside a character class [...], most of these lose their special meaning — only ] \ ^ (at start) and - (between chars) need escaping. Memorizing this list is less useful than knowing the rule: if a character has a special function in regex syntax, escape it to use it literally.