A non-negative integer.

This property returns the number of code units in the string. JavaScript usesUTF-16 encoding, where each Unicode character may be encoded as one or two code units, so it's possible for the value returned bylength 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 2⁵³ - 1 elements, which is the upper limit forprecise 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 2²⁹ - 24 (~1GiB). On 32-bit systems, the maximum length is 2²⁸ - 16 (~512MiB).
• In Firefox, the maximum length is 2³⁰ - 2 (~2GiB). Before Firefox 65, the maximum length was 2²⁸ - 1 (~512MiB).
• In Safari, the maximum length is 2³¹ - 1 (~4GiB).

If you are working with large strings in other encodings (such as UTF-8 files or blobs), note that when you load the data into a JS string, the encoding always becomes UTF-16. The size of the string may be different from the size of the source file.

const str1 = "a".repeat(2 ** 29 - 24); // Successconst str2 = "a".repeat(2 ** 29 - 23); // RangeError: Invalid string lengthconst buffer = new Uint8Array(2 ** 29 - 24).fill("a".codePointAt(0)); // This buffer is 512MiB in sizeconst str = new TextDecoder().decode(buffer); // This string is 1GiB in size

For an empty string,length is 0.

The static propertyString.length is unrelated to the length of strings. It's thearity of theString function (loosely, the number of formal parameters it has), which is 1.

Sincelength counts code units instead of characters, if you want to get the number of characters, you can first split the string with itsiterator, 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

If you want to count characters bygrapheme clusters, useIntl.Segmenter. You can first pass the string you want to split to thesegment() method, and then iterate over the returnedSegments object to get the length:

function getGraphemeCount(str) {  const segmenter = new Intl.Segmenter("en-US", { granularity: "grapheme" });  // The Segments object iterator that is used here iterates over characters in grapheme clusters,  // which may consist of multiple Unicode characters  return [...segmenter.segment(str)].length;}console.log(getGraphemeCount("👨‍👩‍👧‍👧")); // 1

Because string is a primitive, attempting to assign a value to a string'slength property has no observable effect, and will throw instrict mode.

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

• Array:length