notes/node_modules/lodash/size.js

var baseKeys = require('./_baseKeys'),
    getTag = require('./_getTag'),
    isArrayLike = require('./isArrayLike'),
    isString = require('./isString'),
    stringSize = require('./_stringSize');

/** `Object#toString` result references. */
var mapTag = '[object Map]',
    setTag = '[object Set]';

/**
 * Gets the size of `collection` by returning its length for array-like
 * values or the number of own enumerable string keyed properties for objects.
 *
 * @static
 * @memberOf _
 * @since 0.1.0
 * @category Collection
 * @param {Array|Object|string} collection The collection to inspect.
 * @returns {number} Returns the collection size.
 * @example
 *
 * _.size([1, 2, 3]);
 * // => 3
 *
 * _.size({ 'a': 1, 'b': 2 });
 * // => 2
 *
 * _.size('pebbles');
 * // => 7
 */
function size(collection) {
  if (collection == null) {
    return 0;
  }
  if (isArrayLike(collection)) {
    return isString(collection) ? stringSize(collection) : collection.length;
  }
  var tag = getTag(collection);
  if (tag == mapTag || tag == setTag) {
    return collection.size;
  }
  return baseKeys(collection).length;
}

module.exports = size;