Alternation

Q: How deeply does Secrets of the JavaScript Ninja, Second Edition cover alternation?

Defines the pipe operator and demonstrates grouped alternatives and a newline-matching workaround.

As explained in Secrets of the JavaScript Ninja, Second Edition

A regular-expression construct that matches one of several alternative subpatterns.

Alternation lets a regular expression match one of several alternatives. The pipe (`|`) separates them: `/a|b/` matches either `a` or `b`. Group alternatives when a quantifier should apply to them, as in `/(ab)+|(cd)+/`. section 10.2.2

Listing 10.11. Matching all characters, including newlines

 const html = "<b>Hello</b>\n<i>world!</i>";                     #A
 assert(/.*/.exec(html)[0] === "<b>Hello</b>",                   #B
         "A normal capture doesn't handle endlines.");
 assert(/[\S\s]*/.exec(html)[0] ===                              #C
         "<b>Hello</b>\n<i>world!</i>",                          #C
         "Matching everything with a character set.");           #C
 assert(/(?:.|\s)*/.exec(html)[0] ===                            #D
         "<b>Hello</b>\n<i>world!</i>",                          #D
         "Using a non-capturing group to match everything.");    #D

Compare two ways to match across newlines: `/(?:.|\s)*/` uses alternation, while `/[\S\s]*/` uses a character class and is described as the generally optimal solution. section 10.6.1

How Secrets of the JavaScript Ninja, Second Edition covers it

Cover of Secrets of the JavaScript Ninja, Second Edition

liveBook manning.com

Read Secrets of the JavaScript Ninja, Second Edition on liveBook Get the book at manning.com

Related concepts

regular expressionuses · A formal pattern notation that describes sets of strings and enables text to be matched, searched, extracted, or transformed.
set unionproduces · Set union is the operation that produces a set containing every element belonging to at least one of its operand sets.
lookbehind assertionuses · A lookbehind assertion is a regular-expression assertion that checks whether a pattern matches before the current position without consuming the checked input.
cucumber expressionpart of · A Cucumber expression is a pattern syntax for matching step text and converting parameter placeholders into values for step definitions.
alt combinatorequivalent to · A combinator that chooses between two alternative computations, returning the first defined result or otherwise the second.
logical ORimplements · Logical OR is a Boolean disjunction that evaluates to true when at least one operand or condition is true.

This explainer was generated by Manning's knowledge graph from the text of Secrets of the JavaScript Ninja, Second Edition. The section links point to the parts of the book it draws on.