src/get-eaw.js

import defs from "./defs.js";

/**
 * Returns The EAW property of a code point.
 * @private
 * @param {string} codePoint A code point
 * @return {string} The EAW property of the specified code point
 */
function _getEAWOfCodePoint(codePoint) {
  let min = 0;
  let max = defs.length - 1;
  while (min !== max) {
    const i   = min + ((max - min) >> 1);
    const def = defs[i];
    if (codePoint < def.start) {
      max = i - 1;
    }
    else if (codePoint > def.end) {
      min = i + 1;
    }
    else {
      return def.prop;
    }
  }
  return defs[min].prop;
}

/**
 * Returns the EAW property of a character.
 * @param {string} str A string in which the character is contained
 * @param {number} [at = 0] The position (in code unit) of the character in the string
 * @return {string} The EAW property of the specified character
 * @example
 * import { getEAW } from "meaw";
 *
 * // Narrow
 * assert(getEAW("A") === "Na");
 * // Wide
 * assert(getEAW("あ") === "W");
 * assert(getEAW("安") === "W");
 * assert(getEAW("🍣") === "W");
 * // Fullwidth
 * assert(getEAW("Ａ") === "F");
 * // Halfwidth
 * assert(getEAW("ｱ") === "H");
 * // Ambiguous
 * assert(getEAW("∀") === "A");
 * assert(getEAW("→") === "A");
 * assert(getEAW("Ω") === "A");
 * assert(getEAW("Я") === "A");
 * // Neutral
 * assert(getEAW("ℵ") === "N");
 *
 * // a position (in code unit) can be specified
 * assert(getEAW("ℵAあＡｱ∀", 2) === "W");
 */
export function getEAW(str, at) {
  const codePoint = str.codePointAt(at || 0);
  return codePoint === undefined
    ? undefined
    : _getEAWOfCodePoint(codePoint);
}