Function classIndexOf

packages/core/src/render3/styling/class_differ.ts:22–46

(
  className: string,
  classToSearch: string,
  startingIndex: number,
)

 * @returns an index of the located class (or -1 if not found)
 */
export function classIndexOf(
  className: string,
  classToSearch: string,
  startingIndex: number,
): number {
  ngDevMode && assertNotEqual(classToSearch, '', 'can not look for "" string.');
  let end = className.length;
  while (true) {
    const foundIndex = className.indexOf(classToSearch, startingIndex);
    if (foundIndex === -1) return foundIndex;
    if (foundIndex === 0 || className.charCodeAt(foundIndex - 1) <= CharCode.SPACE) {
      // Ensure that it has leading whitespace
      const length = classToSearch.length;
      if (
        foundIndex + length === end ||
        className.charCodeAt(foundIndex + length) <= CharCode.SPACE
      ) {
        // Ensure that it has trailing whitespace
        return foundIndex;
      }
    }
    // False positive, keep searching from where we left off.
    startingIndex = foundIndex + 1;
  }
}