Documentation Index
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Boundary assertions are zero-width positions in the input string — they consume no characters but constrain where a match can occur. TS-Rex exposes four positional assertions that map directly to JavaScript’s regex boundary tokens. These methods are often the first and last calls in a builder chain, anchoring the pattern to the start or end of the string, or to the edges of a word.
startOfInput(): RegexBuilder<TCaptures, TFlags>
^.
When the .multiline() flag is active, ^ matches at the start of each line rather than only the start of the entire string.
import { rx } from '@fajarnugraha37/ts-rex';
const pattern = rx()
.startOfInput()
.oneOrMore(rx().digit())
.compile();
pattern.exec('42abc').isMatch; // true — starts with digits
pattern.exec('abc42').isMatch; // false — does not start with digits
endOfInput(): RegexBuilder<TCaptures, TFlags>
$.
When the .multiline() flag is active, $ matches at the end of each line rather than only the end of the entire string.
const pattern = rx()
.oneOrMore(rx().digit())
.endOfInput()
.compile();
pattern.exec('42').isMatch; // true — ends with digits
pattern.exec('42px').isMatch; // false — trailing non-digit characters
wordBoundary()
wordBoundary(): RegexBuilder<TCaptures, TFlags>
\w) and a non-word character (\W), or the start/end of the string adjacent to a word character. Maps to \b.
// Match the word "cat" but not "catch" or "concatenate"
const pattern = rx()
.wordBoundary()
.literal('cat')
.wordBoundary()
.compile();
pattern.exec('the cat sat').isMatch; // true
pattern.exec('catch the ball').isMatch; // false
nonWordBoundary()
nonWordBoundary(): RegexBuilder<TCaptures, TFlags>
wordBoundary(). Maps to \B.
// Match "cat" only when it appears inside another word
const pattern = rx()
.nonWordBoundary()
.literal('cat')
.nonWordBoundary()
.compile();
pattern.exec('concatenate').isMatch; // true
pattern.exec('the cat').isMatch; // false
Combined example
The most common pattern is to wrap a full expression between startOfInput() and endOfInput() to ensure the regex matches the entire string rather than a substring. This is especially useful when validating structured input like identifiers, tokens, or formatted values.
import { rx } from '@fajarnugraha37/ts-rex';
// Validate a semantic version string: e.g. "1.2.34"
const semver = rx()
.startOfInput()
.capture('major', rx().oneOrMore(rx().digit()))
.literal('.')
.capture('minor', rx().oneOrMore(rx().digit()))
.literal('.')
.capture('patch', rx().oneOrMore(rx().digit()))
.endOfInput()
.compile();
const result = semver.exec('1.2.34');
if (result.isMatch) {
result.major; // "1" — Type: string
result.minor; // "2" — Type: string
result.patch; // "34" — Type: string
}
semver.exec('1.2.34-beta').isMatch; // false — suffix not allowed
semver.exec('v1.2.34').isMatch; // false — prefix not allowed
Without startOfInput() and endOfInput(), the pattern will match a substring anywhere in the input. Add both anchors whenever you are validating that the entire input conforms to a format.
