Set data structure

set.js

class Set{	
	constructor(){
		this.data =  new Array();
	}

	_exist(ele){
		return this.data.indexOf(ele) >= 0
	}

	add(ele){
		if(!this._exist(ele)) this.data.push(ele);
	}

	remove(ele){
		if(this._exist(ele)) this.data.splice(this.data.indexOf(ele) ,1);
	}

	size(){
		let sum  = 0;

		for(let key in this.data) sum += 1
		return sum
	}

	union(otherSet){
		let i = 0, currentLen = this.data.length, otherLen =  otherSet.data.length, newSet  = new Set();

		for(i; i< currentLen; i++) newSet.data[i] =  this.data[i];
		for(i = 0; i < otherLen; i++) newSet.add(otherSet.data[i]); 
		return newSet;
	}

	intersect(otherSet){
		let i = 0, currentLen = this.data.length, newSet =  new Set();

		for(i; i < currentLen; i++){
			let ele =  this.data[i];

			if(otherSet._exist(ele)){
				newSet.add(ele);
			}
		}
		return newSet;
	}

	difference(otherSet){
		let i = 0, currentLen = this.data.length, newSet =  new Set();

		for(i; i < currentLen; i++){
			let ele =  this.data[i];

			if(!otherSet._exist(ele)){
				newSet.add(ele);
			}
		}
		return newSet;
	}

	subSet(otherSet){
		if(this.size() > otherSet.size()) return false;

		let i = 0, currentLen = this.size();	
		for(i; i < currentLen; i++){
			let ele =  this.data[i];

			if(!otherSet._exist(ele)) return false;
		}
		return true;
	}

	display(){
		return `{${this.data.join(", ")}}`;
	}
}