code: function createPartial(func, bitmask, thisArg, partials) {
    var isBind = bitmask & BIND_FLAG,
        Ctor = createCtor(func);
  
    function wrapper() {
      var argsIndex = -1,
          argsLength = arguments.length,
          leftIndex = -1,
          leftLength = partials.length,
          args = Array(leftLength + argsLength),
          fn = this && this !== root && this instanceof wrapper ? Ctor : func;
  
      while (++leftIndex < leftLength) {
        args[leftIndex] = partials[leftIndex];
      }
      while (argsLength--) {
        args[leftIndex++] = arguments[++argsIndex];
      }
      return apply(fn, isBind ? thisArg : this, args);
    }
    return wrapper;
  }
docs: Creates a function that wraps `func` to invoke it with the `this` binding
  of `thisArg` and `partials` prepended to the arguments it receives.
  
  @private
  @param {Function} func The function to wrap.
  @param {number} bitmask The bitmask flags. See `createWrap` for more details.
  @param {*} thisArg The `this` binding of `func`.
  @param {Array} partials The arguments to prepend to those provided to
  the new function.
  @returns {Function} Returns the new wrapped function.