Javascript узнать длину строки

.length

Свойство length хранит длину строки, которое обычно совпадает с количеством символов в ней. Если в строке есть непростые символы, вроде эмодзи, они могут удлинять строку больше, чем на единицу.

Длина пустой строки равна 0.

Пример

Скопировать ссылку «Пример» Скопировано

 const phrase = 'Съешь ещё этих мягких французских булок, да выпей же чаю'console.log(phrase.length)// 56 const empty = ''console.log(empty.length)// 0 const emoji = '👩‍💻'console.log(emoji.length)// 5 🤷‍♂️ const phrase = 'Съешь ещё этих мягких французских булок, да выпей же чаю' console.log(phrase.length) // 56 const empty = '' console.log(empty.length) // 0 const emoji = '👩‍💻' console.log(emoji.length) // 5 🤷‍♂️    Скопировать Скопировано Не удалось скопировать   

Как понять

Скопировать ссылку «Как понять» Скопировано

Строки в JavaScript хранятся в виде последовательности символов в формате UTF-16. UTF-16 использует понятие юнита — одного значения из таблицы UTF-16. Все символы мировых алфавитов представляются в виде одного юнита.

Редкие символы могут использовать несколько юнитов. Если вы решите использовать символы из древнеегипетской письменности, то каждый из них будет занимать два юнита:

 console.log('𓀿'.length)// 2 console.log('𓀿'.length) // 2    Скопировать Скопировано Не удалось скопировать   

Эмодзи состоят из нескольких юнитов. Количество использованных юнитов зависит от эмодзи:

 console.log('👩‍💻'.length)// 5console.log('😀'.length)// 2 console.log('👩‍💻'.length) // 5 console.log('😀'.length) // 2    Скопировать Скопировано Не удалось скопировать   

Источник

String: length

The length data property of a String value contains the length of the string in UTF-16 code units.

Try it

Value

Property attributes of String: length
Writable	no
Enumerable	no
Configurable	no

Description

This property returns the number of code units in the string. JavaScript uses UTF-16 encoding, where each Unicode character may be encoded as one or two code units, so it’s possible for the value returned by length to not match the actual number of Unicode characters in the string. For common scripts like Latin, Cyrillic, wellknown CJK characters, etc., this should not be an issue, but if you are working with certain scripts, such as emojis, mathematical symbols, or obscure Chinese characters, you may need to account for the difference between code units and characters.

The language specification requires strings to have a maximum length of 2 53 — 1 elements, which is the upper limit for precise integers. However, a string with this length needs 16384TiB of storage, which cannot fit in any reasonable device’s memory, so implementations tend to lower the threshold, which allows the string’s length to be conveniently stored in a 32-bit integer.

• In V8 (used by Chrome and Node), the maximum length is 2 29 — 24 (~1GiB). On 32-bit systems, the maximum length is 2 28 — 16 (~512MiB).
• In Firefox, the maximum length is 2 30 — 2 (~2GiB). Before Firefox 65, the maximum length was 2 28 — 1 (~512MiB).
• In Safari, the maximum length is 2 31 — 1 (~4GiB).

For an empty string, length is 0.

The static property String.length is unrelated to the length of strings. It’s the arity of the String function (loosely, the number of formal parameters it has), which is 1.

Since length counts code units instead of characters, if you want to get the number of characters, you can first split the string with its iterator, which iterates by characters:

function getCharacterLength(str)  // The string iterator that is used here iterates over characters, // not mere code units return [. str].length; > console.log(getCharacterLength("A\uD87E\uDC04Z")); // 3 

Examples

Basic usage

const x = "Mozilla"; const empty = ""; console.log(`$x> is $x.length> code units long`); // Mozilla is 7 code units long console.log(`The empty string has a length of $empty.length>`); // The empty string has a length of 0 

Strings with length not equal to the number of characters

const emoji = "😄"; console.log(emoji.length); // 2 console.log([. emoji].length); // 1 const adlam = "𞤲𞥋𞤣𞤫"; console.log(adlam.length); // 8 console.log([. adlam].length); // 4 const formula = "∀𝑥∈ℝ,𝑥²≥0"; console.log(formula.length); // 11 console.log([. formula].length); // 9 

Assigning to length

Because string is a primitive, attempting to assign a value to a string’s length property has no observable effect, and will throw in strict mode.

const myString = "bluebells"; myString.length = 4; console.log(myString); // "bluebells" console.log(myString.length); // 9 

Specifications

Browser compatibility

BCD tables only load in the browser

See also

Found a content problem with this page?

This page was last modified on May 31, 2023 by MDN contributors.

Your blueprint for a better internet.

MDN

Support

Our communities

Developers

Visit Mozilla Corporation’s not-for-profit parent, the Mozilla Foundation.
Portions of this content are ©1998– 2023 by individual mozilla.org contributors. Content available under a Creative Commons license.

Источник

JavaScript String length

ES1 (JavaScript 1997) is fully supported in all browsers:

Chrome	Edge	Firefox	Safari	Opera	IE
Yes	Yes	Yes	Yes	Yes	Yes

COLOR PICKER

Report Error

If you want to report an error, or if you want to make a suggestion, do not hesitate to send us an e-mail:

Thank You For Helping Us!

Your message has been sent to W3Schools.

Top Tutorials

Top References

Top Examples

Get Certified

W3Schools is optimized for learning and training. Examples might be simplified to improve reading and learning. Tutorials, references, and examples are constantly reviewed to avoid errors, but we cannot warrant full correctness of all content. While using W3Schools, you agree to have read and accepted our terms of use, cookie and privacy policy.

Источник