A string is a sequence of characters. In JavaScript, strings are not mutable. Any transfomation of a string, such as slice or concat generates a new string. The JavaScript runtime however may optimize this behavior by mutating strings behind the scenes, when it can be guarenteed that the previous string is not accessible to the programmer. The runtime may also avoid copying slices of a string, or even concatenation of slices of strings, by implementing it as a series of lookups into existing strings. Food for thought.

This package provides functions for generating spaces, querying about a string, comparing strings, getting parts of a string, searching a string, transforming a string or its case, finding ngrams in strings, finding similarity/distance between strings, and array-like functions. All built-in string functions are also included. Finally, constants for ASCII characters, and minimum/maximum code point are included.

▌ 📦 JSR, 📰 Docs.

import * as xstring from "jsr:@nodef/extra-string";

xstring.longestCommonInfix('dismiss', 'mississipi');
// → 'miss'

xstring.longestUncommonInfixes('chocolatier', 'engineer');
// → ['chocolati', 'engine']

xstring.toKebabCase('Malwa Plateau');
// → 'malwa-plateau'

'6.626 x 10' + xstring.toSuperscript('-34');
// → '6.626 x 10⁻³⁴' (Planck's constant)

xstring.tverskyDistance('pikachu', 'raichu', 3, 0.2, 0.4);
// → 0.6666666666666667

Index

Name	Description
toKebabCase	Convert a string to kebab-case.
toSnakeCase	Convert a string to snake-case.
toCamelCase	Convert a string to camel-case.
toPascalCase	Convert a string to pascal-case.
toSlugCase	Convert a string to slug-case (URL-friendly kebab-case).
toWords	Split a string into words, after de-casing it.
toBaseline	Convert a string to baseline characters (limited support).
toSuperscript	Convert a string to superscript characters (limited support).
toSubscript	Convert a string to superscript characters (limited support).
ngrams	Get n-grams of a string.
uniqueNgrams	Find unique n-grams of a string.
countNgrams	Count the total number of n-grams of a string.
countUniqueNgrams	Count the total number of unique n-grams of a string.
countEachNgram	Count each n-gram of a string.
matchingNgrams	Get matching n-grams between strings.
uniqueMatchingNgrams	Get unique matching n-grams between strings.
countMatchingNgrams	Count the total number of matching n-grams between strings.
countEachMatchingNgram	Count each matching n-gram between strings.
countUniqueMatchingNgrams	Count the total number of unique matching n-grams between strings.
euclideanDistance	Get euclidean distance between strings.
hammingDistance	Get hamming distance between strings.
jaccardIndex	Get jaccard index between strings.
jaccardDistance	Get jaccard distance between strings.
sorensenDiceIndex	Get Sørensen-Dice index between strings.
sorensenDiceDistance	Get Sørensen-Dice distance between strings.
tverskyIndex	Get Tversky index between strings.
tverskyDistance	Get Tversky distance between strings.
jaroSimilarity	Get Jaro similarity between strings.
jaroDistance	Get Jaro distance between strings.
jaroWinklerSimilarity	Get Jaro-Winkler similarity between strings.
jaroWinklerDistance	Get Jaro-Winkler distance between strings.
levenshteinDistance	Get Levenshtein distance between strings.
damerauLevenshteinDistance	Get Damerau–Levenshtein distance between strings.
longestCommonInfix	Get the longest common infix between strings.
longestCommonPrefix	Get the longest common prefix of strings.
longestCommonSuffix	Get the longest common suffix of strings.
longestUncommonInfixes	Get the longest uncommon infixes of strings.
get	Get character at a given index in string.
getAll	Get characters at indices.
set	Write a substring at specified index in string.
begin	Get leftmost part of string.
middle	Get a portion of string from middle.
end	Get rightmost part of string.
fromCharCode	Get characters whose UTF-16 code units are given.
fromCodePoint	Get characters whose unicode code points are given.
concat	Combine multiple strings into one.
repeat	Repeat string given number of times.
valueOf	Get primitive value of string object.
length	Get length of string.
charAt	Get character at given index in string.
charCodeAt	Get UTF-16 code unit of a character in string.
codePointAt	Get unicode code point of a character in string.
localeCompare	Compare two strings in the current or given locale.
includes	Check if string has a given infix.
startsWith	Check if string has a given prefix.
endsWith	Check if string has a given suffix.
indexOf	Get first index of a given infix in string.
lastIndexOf	Get last index of a given infix in string.
search	Get first index of regular expression match in string.
match	Get results of matching string with regular expression.
matchAll	Get detailed results of matching string with regular expression.
toString	Get string representation of string.
slice	Extract section of string.
substring	Extract section of string.
split	Split string by a given separator into substrings.
trimStart	Remove whitespace from begining of string.
trimEnd	Remove whitespace from end of string.
trim	Remove whitespace from begining and end of string.
padStart	Pad start of string to fit a desired length.
padEnd	Pad end of string to fit a desired length.
toUpperCase	Convert string to upper case.
toLocaleUpperCase	Convert string to upper case, as per locale-specific case mappings.
toLowerCase	Convert string to lower case.
toLocaleLowerCase	Convert string to lower case, as per locale-specific case mappings.
replace	Replace first match of given pattern by replacement.
normalize	Normalize string by given form, as per Unicode Standard Annex #15.
of	Create string from arguments, like Array.of().
from	Create string from iterable, like Array.from().
splice	Remove/replace characters in a string.
reverse	Reverse a string.
sort	Arrange characters in an order.
filter	Filter characters which pass a test.
spaces	Get a string of spaces.
is	Check if value is a string.
isEmpty	Check if string is empty.
isCharacter	Check if string is a character.
index	Get non-negative index within string.
indexRange	Get non-negative index range within string.
codePointRange	Get unicode code point range of string.
compare	Compare two strings.
isEqual	Check if two strings are equal.
DIGITS	Decimal digits 0-9.
OCT_DIGITS	Octal digits 0-7.
HEX_DIGITS	Hexadecimal digits 0-9, A-F, a-f.
UPPERCASE	English letters A-Z.
LOWERCASE	English letters a-z.
LETTERS	Combination of uppercase, lowercase english letters.
PUNCTUATION	Punctuation symbols (ASCII).
WHITESPACE	The string "\t\n\x0b\x0c\r ".
PRINTABLE	Combination of digits, letters, punctuation, and whitespace (ASCII).
MIN_CODE_POINT	Minimum unicode code point.
MAX_CODE_POINT	Maximum unicode code point.

References

• MDN Web docs
• Lodash documentation
• natural package by Chris Umbel and contributors
• esrever package by Mathias Bynens and contributors
• js-string-compression package by Chen Caishun
• @stdlib/string-base-trim package by @stdlib-js
• How do you reverse a string in-place in JavaScript?

License

As of 26 June 2025, this project is licensed under AGPL-3.0. Previous versions remain under MIT.