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- 'use strict';
- var getBuiltIn = require('../internals/get-built-in');
- var uncurryThis = require('../internals/function-uncurry-this');
- var aCallable = require('../internals/a-callable');
- var lengthOfArrayLike = require('../internals/length-of-array-like');
- var toObject = require('../internals/to-object');
- var arraySpeciesCreate = require('../internals/array-species-create');
- var Map = getBuiltIn('Map');
- var MapPrototype = Map.prototype;
- var mapForEach = uncurryThis(MapPrototype.forEach);
- var mapHas = uncurryThis(MapPrototype.has);
- var mapSet = uncurryThis(MapPrototype.set);
- var push = uncurryThis([].push);
- // `Array.prototype.uniqueBy` method
- // https://github.com/tc39/proposal-array-unique
- module.exports = function uniqueBy(resolver) {
- var that = toObject(this);
- var length = lengthOfArrayLike(that);
- var result = arraySpeciesCreate(that, 0);
- var map = new Map();
- var resolverFunction = resolver != null ? aCallable(resolver) : function (value) {
- return value;
- };
- var index, item, key;
- for (index = 0; index < length; index++) {
- item = that[index];
- key = resolverFunction(item);
- if (!mapHas(map, key)) mapSet(map, key, item);
- }
- mapForEach(map, function (value) {
- push(result, value);
- });
- return result;
- };
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