forEach.js

/**
 * Maps a callback to an element in an array-like object
 * Basically a copy of underscore's _.each
 * source: http://underscorejs.org/docs/underscore.html#section-20
 */
export function forEach(obj, iteratee, context) {
  let ctx = this;

  const isObject = function(obj) {
    var type = typeof obj;
    return type === 'function' || type === 'object' && !!obj;
  };

  const has = function(obj, key) {
    return obj != null && hasOwnProperty.call(obj, key);
  };

  const _keys = function(obj) {
    if (!isObject(obj)) return [];
    if (Object.keys) return Object.keys(obj);
    var keys = [];
    for (var key in obj) if (has(obj, key)) keys.push(key);

    if (hasEnumBug) collectNonEnumProps(obj, keys);
    return keys;
  };

  // source: https://github.com/darsain/isarraylike/blob/master/index.js
  const isArrayLike = function(value, complex) {
    return value
      && typeof value === 'object'
      && typeof value.length === 'number'
      && value.length >= 0
      && value.length % 1 === 0
      && (!complex || typeof value.splice === 'function');
  }

  if (context !== void 0) {
    ctx = context;
  }

  if (isArrayLike(obj)) {
    for (let i = 0, length = obj.length; i < length; i++) {
      iteratee.call(ctx, obj[i], i, obj);
    }
  } else {
    const keys = _keys(obj);
    for (let i = 0, length = keys.length; i < length; i++) {
      iteratee.call(ctx, obj[keys[i]], keys[i], obj);
    }
  }

  return obj;
}