How can I truncate a string accounting for locale?

JavaScript, String · Dec 4, 2022

Breaking a string into words is not the easiest, neither is finding a good place to add an ellipsis. Part of the problem is recognizing word boundaries and words themselves. Luckily Intl.Segmenter is a relatively new object that enables locale-sensitive text segmentation.

Intl.Segmenter allows you to specify a locale and a granularity option to specify how a string should be segmented. The granularity option can be set to 'grapheme', 'word' or 'sentence' according to your needs. Using Intl.Segmenter.prototype.segment() on a string returns an iterable Segments object. This can then be used to find the correct index to split a string without being in the middle of a word or a sentence.

const str =
  'The quick brown fox jumps over the lazy dog. The jay, pig, fox, zebra and my wolves quack!';
const cutOff = 50;

const wordSegmenter = new Intl.Segmenter('en-US', { granularity: 'word' });
const sentenceSegmenter = new Intl.Segmenter('en-US', {
  granularity: 'sentence',

let lastWordBreak = -1;
for (let word of wordSegmenter.segment(str)) {
  if (word.isWordLike) continue;
  if (word.index >= cutOff) break;
  lastWordBreak = word.index;
str.slice(0, lastWordBreak) + '...';
// 'The quick brown fox jumps over the lazy dog. The...'

let lastSentenceBreak = -1;
for (let sentence of sentenceSegmenter.segment(str)) {
  if (
    lastSentenceBreak !== -1 &&
    sentence.index + sentence.segment.length >= cutOff
  lastSentenceBreak = sentence.index + sentence.segment.length;
str.slice(0, lastSentenceBreak).trim().slice(0, -1) + '...';
// 'The quick brown fox jumps over the lazy dog...'

Note that the Intl.Segmenter object is not yet supported in all environments at the time of writing (December, 2022). Namely, Firefox has yet to implement it, while Node.js has only started supporting it since version 16.0.0.

Written by Angelos Chalaris

I'm Angelos Chalaris, a JavaScript software engineer, based in Athens, Greece. The best snippets from my coding adventures are published here to help others learn to code.

If you want to keep in touch, follow me on GitHub or Twitter.

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