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'use strict';
var $ = require('../internals/export');
var toLength = require('../internals/to-length');
var toObject = require('../internals/to-object');
var getBuiltIn = require('../internals/get-built-in');
var arraySpeciesCreate = require('../internals/array-species-create');
var addToUnscopables = require('../internals/add-to-unscopables');
var push = [].push;
// `Array.prototype.uniqueBy` method
// https://github.com/tc39/proposal-array-unique
$({ target: 'Array', proto: true }, {
uniqueBy: function uniqueBy(resolver) {
var that = toObject(this);
var length = toLength(that.length);
var result = arraySpeciesCreate(that, 0);
var Map = getBuiltIn('Map');
var map = new Map();
var resolverFunction, index, item, key;
if (typeof resolver == 'function') resolverFunction = resolver;
else if (resolver == null) resolverFunction = function (value) {
return value;
};
else throw new TypeError('Incorrect resolver!');
for (index = 0; index < length; index++) {
item = that[index];
key = resolverFunction(item);
if (!map.has(key)) map.set(key, item);
}
map.forEach(function (value) {
push.call(result, value);
});
return result;
}
});
addToUnscopables('uniqueBy');
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