2 var toLength = require('../internals/to-length');
3 var toObject = require('../internals/to-object');
4 var getBuiltIn = require('../internals/get-built-in');
5 var arraySpeciesCreate = require('../internals/array-species-create');
9 // `Array.prototype.uniqueBy` method
10 // https://github.com/tc39/proposal-array-unique
11 module.exports = function uniqueBy(resolver) {
12 var that = toObject(this);
13 var length = toLength(that.length);
14 var result = arraySpeciesCreate(that, 0);
15 var Map = getBuiltIn('Map');
17 var resolverFunction, index, item, key;
18 if (typeof resolver == 'function') resolverFunction = resolver;
19 else if (resolver == null) resolverFunction = function (value) {
22 else throw new TypeError('Incorrect resolver!');
23 for (index = 0; index < length; index++) {
25 key = resolverFunction(item);
26 if (!map.has(key)) map.set(key, item);
28 map.forEach(function (value) {
29 push.call(result, value);