Time complexity of the includes method in JavaScript

Spec describes this function as linear search. Array.prototype.includes

1. Let O be ? ToObject(this value).

2. Let len be ? ToLength(? Get(O, "length")).

3. If len is 0, return false.
4. Let n be ? ToInteger(fromIndex). (If fromIndex is undefined, this step produces the value 0.)
5. If n ≥ 0, then Let k be n.
6. Else n < 0, Let k be len + n. If k < 0, let k be 0.
7. Repeat, while k < len ... Increase k by 1.

Which is quite a reasonable choice in general case (list is not sorted, list is not uniform, you do not maintain additional datastructures along with the list itself).

as my list is not sorted so i have create a dictionary and put values into it after checking if value present in it or not . Here in this dictionary my value and key are same .

var   arrayOfHashMap = {};/*is a dictionary,arrayOfValue is a list*/    if(arrayOfHashMap[hash_value] !=hash_value){                               arrayOfValue.push(hash_value);                                arrayOfHashMap[hash_value]=hash_value;                        }

in this case I search values in o(1) time and put them in arrayOfValue