escape-unicode/src/parse.js

Escapes Unicode characters

/*
 * Copyright (C) 2018 Alasdair Mercer
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

'use strict';

/**
 * The available digits for hexadecimal values.
 *
 * @type {string[]}
 */
const hexDigits = '0123456789abcdef'.split('');

/**
 * Parses the specified Unicode character found within the input string and calculate the hexadecimal representation of
 * its Unicode code point.
 *
 * @param {string} ch - the character to be parsed to calculate the hexadecimal segment of the Unicode escape
 * @return {string} The calculated Unicode code point in its hexadecimal representation.
 */
function parse(ch) {
  const code = ch.codePointAt(0);

  return toHexDigit((code >> 12) & 15) +
    toHexDigit((code >> 8) & 15) +
    toHexDigit((code >> 4) & 15) +
    toHexDigit(code & 15);
}

/**
 * Converts the specified <code>nibble</code> into a hexadecimal digit.
 *
 * @param {number} nibble - the nibble to be converted
 * @return {string} The single-digit hexadecimal string.
 */
function toHexDigit(nibble) {
  return hexDigits[nibble & 15];
}

module.exports = parse;