String.fromCharCode() static method returns a string created from the specified sequence of UTF-16 code units.
String.fromCharCode() String.fromCharCode(num1) String.fromCharCode(num1, num2) String.fromCharCode(num1, num2, /* …, */ numN)
A number between
0xFFFF) representing a UTF-16 code unit. Numbers greater than
0xFFFFare truncated to the last 16 bits. No validity checks are performed.
A string of length
N consisting of the
N specified UTF-16 code units.
fromCharCode() is a static method of
String, you always use it as
String.fromCharCode(), rather than as a method of a
String value you created.
Unicode code points range from
charCodeAt() always returns a value that is less than
65536, because the higher code points are represented by a pair of 16-bit surrogate pseudo-characters. Therefore, in order to produce a full character with value greater than
65535, it is necessary to provide two code units (as if manipulating a string with two characters). For information on Unicode, see UTF-16 characters, Unicode code points, and grapheme clusters.
fromCharCode() only works with 16-bit values (same as the
\u escape sequence), a surrogate pair is required in order to return a supplementary character. For example, both
String.fromCharCode(0xd83c, 0xdf03) and
"\ud83c\udf03" return code point
U+1F303 "Night with Stars". While there is a mathematical relationship between the supplementary code point value (e.g.
0x1f303) and both surrogate values that represent it (e.g.,
0xdf03), it does require an extra step to either calculate or look up the surrogate pair values every time a supplementary code point is to be used. For this reason, it's more convenient to use
String.fromCodePoint(), which allows for returning supplementary characters based on their actual code point value. For example,
String.fromCodePoint(0x1f303) returns code point
U+1F303 "Night with Stars".
BMP characters, in UTF-16, use a single code unit:
String.fromCharCode(65, 66, 67); // returns "ABC" String.fromCharCode(0x2014); // returns "—" String.fromCharCode(0x12014); // also returns "—"; the digit 1 is truncated and ignored String.fromCharCode(8212); // also returns "—"; 8212 is the decimal form of 0x2014
Supplementary characters, in UTF-16, require two code units (i.e. a surrogate pair):
String.fromCharCode(0xd83c, 0xdf03); // Code Point U+1F303 "Night with String.fromCharCode(55356, 57091); // Stars" === "\uD83C\uDF03" String.fromCharCode(0xd834, 0xdf06, 0x61, 0xd834, 0xdf07); // "\uD834\uDF06a\uD834\uDF07"
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