Regular Expressions | JavaScript Lesson

Lesson content

Read, practise, then check your understanding

Regular expressions are concise pattern programs. Literals suit fixed patterns; new RegExp supports runtime construction and requires careful escaping.

Structured matching

const pattern = /^(?<user>[a-z0-9._-]+)@(?<host>[a-z0-9.-]+)$/iu;
const match = pattern.exec(input);
if (match) console.log(match.groups.user, match.groups.host);

Classes, quantifiers, groups, alternation, anchors, and lookarounds express constraints. Flags include global, case-insensitive, multiline, dotAll, Unicode, and sticky behavior. A global regex mutates lastIndex. Escape user-supplied fragments and avoid nested ambiguous quantifiers that enable catastrophic backtracking. Use a parser for complex grammars.

Knowledge check

Answer every question correctly to complete this chapter.

Which statement best describes regular expression?

Which JavaScript term matches this description: A pattern language for searching and transforming text.

Which statement best describes capture group?

Which JavaScript term matches this description: A parenthesized subpattern whose match is retained.

Which statement best describes character class?

Which JavaScript term matches this description: A pattern matching one character from a defined set.

Which statement best describes global flag?

Which JavaScript term matches this description: The g flag enabling repeated matches and stateful lastIndex behavior.

Which statement best describes Unicode flag?

Which JavaScript term matches this description: The u flag enabling Unicode-aware pattern interpretation.

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