Function flatten

MathBox/mathbox-bundle.js:39496–39507

* Flattens a nested array (the nesting can be to any depth). If `isShallow` * is truey, the array will only be flattened a single level. If a callback * is provided each element of the array is passed through the callback before * flattening. The callback is bound to `thisArg` and inv

(array, isShallow, callback, thisArg)

     * // => ['hoppy', 'baby puss', 'dino']
     */
    function flatten(array, isShallow, callback, thisArg) {
      // juggle arguments
      if (typeof isShallow != 'boolean' && isShallow != null) {
        thisArg = callback;
        callback = (typeof isShallow != 'function' && thisArg && thisArg[isShallow] === array) ? null : isShallow;
        isShallow = false;
      }
      if (callback != null) {
        array = map(array, callback, thisArg);
      }
      return baseFlatten(array, isShallow);
    }

    /**
     * Gets the index at which the first occurrence of `value` is found using