Source: util/string.ts

  1. /**
  2.  * @author Michael Hasenstein <hasenstein@yahoo.com>
  3.  * @copyright REFINIO GmbH 2020
  4.  * @license CC-BY-NC-SA-2.5; portions MIT License
  5.  * @version 0.0.1
  6.  */
  8. /**
  9.  * Helper function(s) for strings.
  10.  * @module
  11.  */
  13. import {createError} from '../errors';
  14. import {isInteger} from './type-checks-basic';
  16. /**
  17.  * **JS RUNTIME OPTIMIZATION PREVENTION HACK**
  18.  *
  19.  * Workaround for {@link https://bugs.chromium.org/p/v8/issues/detail?id=2869}
  20.  *
  21.  * This is the same as the standard string function `substr`, but it forces the JS runtime to
  22.  * allocate new memory.
  23.  *
  24.  * Modern runtimes internally don't always allocate new memory, instead they keep a reference to
  25.  * the original string as well as start and end within that string if the runtime sees a
  26.  * read-only use of the sub string.
  27.  * @static
  28.  * @param {string} s - A string
  29.  * @param {number} start - A non-negative integer start position
  30.  * @param {number} [length=s.length-start] - A non-negative length. If omitted, it is calculated
  31.  * as `s.length - start`
  32.  * @returns {string}
  33.  */
  34. export function substrForceMemCopy(
  35.     s: string,
  36.     start: number,
  37.     length: number = s.length - start
  38. ): string {
  39.     // Because of the charAt() this case would not work and needs to be handled separately now.
  40.     // This must happen BEFORE the error-throwing parameter checks in order to work like the
  41.     // original substr() for these cases!
  42.     if (start > s.length || length === 0) {
  43.         return '';
  44.     }
  46.     // We don't recreate the exact same behavior of the original substr() function, so we must
  47.     // exclude negative values
  48.     if (!isInteger(start) || !isInteger(length) || start < 0 || length < 0) {
  49.         throw createError('US-SSFMC1', {s, start, length});
  50.     }
  52.     // Adding the last character in a string concatenation operation *should* work around any
  53.     // current string operation optimizations and force the runtime to allocate new memory for the
  54.     // resulting string.
  55.     return s.substr(start, length - 1) + s.charAt(start + length - 1);
  56. }