StringprototypecodePointAt

String.prototype.codePointAt is a JavaScript method that returns the Unicode code point value at a given position in a string. It is part of the String.prototype object and was introduced with ECMAScript 2015 (ES6) to provide robust handling of characters outside the Basic Multilingual Plane through proper treatment of UTF-16 surrogate pairs.

The method accepts a single argument, position, which is coerced to an integer index. If the index is within the bounds of the string, it returns a number representing the code point at that position. If the index is outside the string’s length, the result is undefined. When the position points to the first code unit of a surrogate pair, codePointAt returns the full Unicode code point value represented by the pair. If the position points to the second code unit of a surrogate pair (the low surrogate), the method returns the code unit value of that single unit, not the combined code point.

Common use cases include obtaining exact code point values for individual characters, iterating over strings by code point rather than by UTF-16 code units, and implementing custom processing that must distinguish characters outside the BMP from single-unit code units. Since codePointAt cooperates with surrogate pairs, it supports accurate handling of characters such as emoji and less common scripts.

Examples:

- "ABC".codePointAt(0) yields 65.

- "💩".codePointAt(0) yields 0x1F4A9 (128169 in decimal).

- "💩".codePointAt(1) yields 0xDCA9 (56489 in decimal).

- "ABC".codePointAt(3) yields undefined.