Simple and naive implementation of array without duplicated items; Python set-like data structure written in JS. #help #wanted

set.js

var jsSet = { item: 0 };  // use Object key as set item

item = 'setItem'
if (!(item in jsSet)) {  // if item not in jsSet
    jsSet[item] = 1;  // save item with meaningless value
}

sessionStorage.setItem('jsSet', JSON.stringify(Object.keys(usages)))  // save into sessionStorage