lodash/spread.js

import apply from './_apply';
import arrayPush from './_arrayPush';
import rest from './rest';
import toInteger from './toInteger';

/** Used as the `TypeError` message for "Functions" methods. */
var FUNC_ERROR_TEXT = 'Expected a function';

/* Built-in method references for those with the same name as other `lodash` methods. */
var nativeMax = Math.max;

/**
 * Creates a function that invokes `func` with the `this` binding of the created
 * function and an array of arguments much like [`Function#apply`](https://es5.github.io/#x15.3.4.3).
 *
 * **Note:** This method is based on the [spread operator](https://mdn.io/spread_operator).
 *
 * @static
 * @memberOf _
 * @category Function
 * @param {Function} func The function to spread arguments over.
 * @param {number} [start=0] The start position of the spread.
 * @returns {Function} Returns the new function.
 * @example
 *
 * var say = _.spread(function(who, what) {
 *   return who + ' says ' + what;
 * });
 *
 * say(['fred', 'hello']);
 * // => 'fred says hello'
 *
 * var numbers = Promise.all([
 *   Promise.resolve(40),
 *   Promise.resolve(36)
 * ]);
 *
 * numbers.then(_.spread(function(x, y) {
 *   return x + y;
 * }));
 * // => a Promise of 76
 */
function spread(func, start) {
  if (typeof func != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  start = start === undefined ? 0 : nativeMax(toInteger(start), 0);
  return rest(function(args) {
    var array = args[start],
        otherArgs = args.slice(0, start);

    if (array) {
      arrayPush(otherArgs, array);
    }
    return apply(func, this, otherArgs);
  });
}

export default spread;