JavaScript’s String.length counts UTF-16 code units—not necessarily Unicode code points, visible characters, or words. Use it for JavaScript’s string-indexing unit; use code-point iteration, Intl.Segmenter, or a separate byte measurement when your task calls for a different unit.
What does String.length count?
JavaScript strings are represented as sequences of UTF-16 code units. The length property returns the number of those units. A Unicode code point in the Basic Multilingual Plane typically uses one code unit; a supplementary code point uses a pair called a surrogate pair, so one code point can contribute two to length. MDN explains this distinction in its documentation for String.length.
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"A".length; // 1
"😄".length; // 2That result is not a JavaScript error: it reflects the string’s UTF-16 representation. It simply may not answer a question about how many code points or user-perceived characters the text contains.
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Which counting method should you use?
| Need | Method | What it counts |
|---|---|---|
| JavaScript string indexing or UTF-16 units | text.length |
UTF-16 code units; a supplementary code point counts as two. |
| Unicode code points | [...text].length |
Code points, keeping a valid surrogate pair together, but not combining marks or multi-code-point emoji sequences. |
| Approximate user-perceived characters | Intl.Segmenter with granularity: "grapheme" |
Grapheme clusters, which can keep combining marks and joined emoji sequences together. |
| Words in a locale-sensitive text | Intl.Segmenter with granularity: "word" |
Segments marked as word-like by the segmenter. |
| Encoded storage or transmission size | Measure bytes using the required encoding | Bytes, not characters or grapheme clusters. |
How do you count Unicode code points?
String iteration treats a valid surrogate pair as one code point, so spreading a string into an array and reading its length gives a code-point count:
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const codePointCount = (text) => [...text].length;This is useful when the requirement specifically concerns code points. It does not count user-perceived characters in every case. For example, a letter followed by a combining accent can contain two code points while appearing as one character. Likewise, many emoji—including joined sequences and flags—are formed from multiple code points.
MDN’s JavaScript String guide discusses code points, surrogate pairs, and emoji sequences. For default rules defining grapheme, word, and sentence boundaries, see the Unicode Consortium’s Unicode Text Segmentation, UAX #29, Unicode 18.0.0, Version 49 (2026-09-01).
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How do you count user-perceived characters, including emoji?
Use Intl.Segmenter with grapheme granularity when a limit or display reports approximate user-perceived characters. A grapheme cluster may consist of several code points, such as a base letter with a combining mark or an emoji joined to another emoji.
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const graphemeSegmenter = new Intl.Segmenter("en", {
granularity: "grapheme",
});
const graphemeCount = (text) =>
[...graphemeSegmenter.segment(text)].length;Choose a locale appropriate to the content or application, and check that the target JavaScript runtime supports the needed Intl.Segmenter behavior. MDN describes grapheme-level segmentation with Intl.Segmenter as useful for counting characters. Grapheme clusters are a practical approximation of user-perceived characters, not a measure of rendered width: fonts and layout can make clusters occupy different amounts of space.
How do you count words reliably?
Splitting on whitespace is a quick approximation for text that uses spaces between words, but it is not a general word-counting rule. Punctuation and writing systems that do not separate words with spaces can make whitespace splitting misleading. Use word segmentation and count only segments whose isWordLike property is true:
const wordSegmenter = new Intl.Segmenter("en", {
granularity: "word",
});
const wordCount = (text) =>
[...wordSegmenter.segment(text)]
.filter((part) => part.isWordLike).length;Set the locale to suit the text or application rather than assuming one segmentation choice is correct for every language. The MDN internationalization guide explains word segmentation and why whitespace splitting has limits.
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What if you need a byte limit or display width?
Neither text.length nor a grapheme count gives the number of bytes in an encoded string. If a database, protocol, or API imposes a byte limit, measure the text in the encoding that limit specifies. Similarly, grapheme count does not calculate visual width; rendered width depends on presentation as well as the text’s segmentation.
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