Background

In JavaScript there is not always a one-to-one relationship between string characters and what a user would call a separate visual "letter". Some symbols are represented by several characters. This can cause issues when splitting strings and inadvertently cutting a multi-char letter in half, or when you need the actual number of letters in a string.

For example, emoji characters like "🌷","🎁","💩","😜" and "👍" are represented by two JavaScript characters each (high surrogate and low surrogate). That is,

``javascript
"🌷".length == 2
`
The combined emoji are even longer:
`javascript
"🏳️‍🌈".length == 6
`

What's more, some languages often include combining marks - characters that are used to modify the letters before them. Common examples are the German letter ü and the Spanish letter ñ. Sometimes they can be represented alternatively both as a single character and as a letter + combining mark, with both forms equally valid:

`javascript
var two = "ñ"; // unnormalized two-char n+◌̃ , i.e. "\u006E\u0303";
var one = "ñ"; // normalized single-char, i.e. "\u00F1"
console.log(one!=two); // prints 'true'
`

Unicode normalization, as performed by the popular punycode.js library or ECMAScript 6's String.normalize, can sometimes fix those differences and turn two-char sequences into single characters. But it is not enough in all cases. Some languages like Hindi make extensive use of combining marks on their letters, that have no dedicated single-codepoint Unicode sequences, due to the sheer number of possible combinations.
For example, the Hindi word "अनुच्छेद" is comprised of 5 letters and 3 combining marks:

अ + न + ु + च + ् + छ + े + द

which is in fact just 5 user-perceived letters:

अ + नु + च् + छे + द

and which Unicode normalization would not combine properly.
There are also the unusual letter+combining mark combinations which have no dedicated Unicode codepoint. The string Z͑ͫ̓ͪ̂ͫ̽͏̴̙̤̞͉͚̯̞̠͍A̴̵̜̰͔ͫ͗͢L̠ͨͧͩ͘G̴̻͈͍͔̹̑͗̎̅͛́Ǫ̵̹̻̝̳͂̌̌͘ obviously has 5 separate letters, but is in fact comprised of 58 JavaScript characters, most of which are combining marks.

Enter the grapheme-splitter.js library. It can be used to properly split JavaScript strings into what a human user would call separate letters (or "extended grapheme clusters" in Unicode terminology), no matter what their internal representation is. It is an implementation on the Default Grapheme Cluster Boundary of UAX #29.

Installation

You can use the index.js file directly as-is. Or you you can install grapheme-splitter to your project using the NPM command below:

`
$ npm install --save grapheme-splitter
`

Tests

To run the tests on grapheme-splitter, use the command below:

`
$ npm test
`

Usage

Just initialize and use:

`javascript
var splitter = new GraphemeSplitter();

// split the string to an array of grapheme clusters (one string each)
var graphemes = splitter.splitGraphemes(string);

// iterate the string to an iterable iterator of grapheme clusters (one string each)
var graphemes = splitter.iterateGraphemes(string);

// or do this if you just need their number
var graphemeCount = splitter.countGraphemes(string);
`

Examples

`javascript
var splitter = new GraphemeSplitter();

// plain latin alphabet - nothing spectacular
splitter.splitGraphemes("abcd"); // returns ["a", "b", "c", "d"]

// two-char emojis and six-char combined emoji
splitter.splitGraphemes("🌷🎁💩😜👍🏳️‍🌈"); // returns ["🌷","🎁","💩","😜","👍","🏳️‍🌈"]

// diacritics as combining marks, 10 JavaScript chars
splitter.splitGraphemes("Ĺo͂řȩm̅"); // returns ["Ĺ","o͂","ř","ȩ","m̅"]

// individual Korean characters (Jamo), 4 JavaScript chars
splitter.splitGraphemes("뎌쉐"); // returns ["뎌","쉐"]

// Hindi text with combining marks, 8 JavaScript chars
splitter.splitGraphemes("अनुच्छेद"); // returns ["अ","नु","च्","छे","द"]

// demonic multiple combining marks, 75 JavaScript chars
splitter.splitGraphemes("Z͑ͫ̓ͪ̂ͫ̽͏̴̙̤̞͉͚̯̞̠͍A̴̵̜̰͔ͫ͗͢L̠ͨͧͩ͘G̴̻͈͍͔̹̑͗̎̅͛́Ǫ̵̹̻̝̳͂̌̌͘!͖̬̰̙̗̿̋ͥͥ̂ͣ̐́́͜͞"); // returns ["Z͑ͫ̓ͪ̂ͫ̽͏̴̙̤̞͉͚̯̞̠͍","A̴̵̜̰͔ͫ͗͢","L̠ͨͧͩ͘","G̴̻͈͍͔̹̑͗̎̅͛́","Ǫ̵̹̻̝̳͂̌̌͘","!͖̬̰̙̗̿̋ͥͥ̂ͣ̐́́͜͞"]
`

TypeScript

Grapheme splitter includes TypeScript declarations.

`typescript
import GraphemeSplitter = require('grapheme-splitter')

const splitter = new GraphemeSplitter()

const split: string[] = splitter.splitGraphemes('Z͑ͫ̓ͪ̂ͫ̽͏̴̙̤̞͉͚̯̞̠͍A̴̵̜̰͔ͫ͗͢L̠ͨͧͩ͘G̴̻͈͍͔̹̑͗̎̅͛́Ǫ̵̹̻̝̳͂̌̌͘!͖̬̰̙̗̿̋ͥͥ̂ͣ̐́́͜͞')
``

Acknowledgements

This library is heavily influenced by Devon Govett's excellent grapheme-breaker CoffeeScript library at https://github.com/devongovett/grapheme-breaker with an emphasis on ease of integration and pure JavaScript implementation.