underscorePractise4.js

(function() {
	var log = function(x) {console.log(x)}

	var a = [1, 2, 5];
	var b = [5, 2, 8];
	var x, y, z;

	z = _.difference(a, b);
	//log(z); // [1]

	y = _.intersection(a, b);
	//log(y); // [2, 5]

	x = _.union(a, b);
	//log(x); // [1, 2, 5, 8]

	var u = _.unique([2, 5, 10, 5, 10]);
	// log(u);

	// union by js
	var sumAry = [], 
		totalLen = a.length + b.length;
		eachAry = [a, b], 
		eachLen = [a.length, b.length];

	var uniqueCheck = function(a, s) {
		for (var i = 0; i < a.length; i++) {
			if(a[i] == s) {
				return false;
			}
		}
		return true;
	};

	for(var i = 0; i < totalLen; i++) {
		for(var j = 0; j < eachLen[i]; j++) {
			if( uniqueCheck(sumAry, eachAry[i][j]) ) {
				sumAry.push(eachAry[i][j]);
			}
		}
	}
	//log(sumAry);

	// intersection by js
	var interAry = [];

	for (var i = 0; i < a.length; i++) {
		for (var j = 0; j < b.length; j++) {
			if(a[i] == b[j]){
				interAry.push(a[i]);
				break;
			}
		} 
	}
	//log(interAry);

	// difference by js
	var difAry = [];

	var difCheck = function(a){
		for(var i = 0; i < b.length; i++) {
			if(a == b[i]) {
				return false;
			}
		}
		return true;
	};
	for (var i = 0; i < a.length; i++) {
		if( difCheck(a[i]) ) {
			difAry.push(a[i]);
		}
	}
	//log(difAry);

	// unique by js
	var nums = [2, 3, 9, 10, 2, 9],
		uniqueAry = [];

	var isUnique = function(a, e) {
		for (var i = 0; i < a.length; i++) {
			if(a[i] == e) {
				return false;
			}
		}
		return true;
	};

	for(var i = 0; i < nums.length; i++) {
		if( isUnique(uniqueAry, nums[i]) ) {
			uniqueAry.push(nums[i]);
		}
	}
	//log(uniqueAry); // [2, 3, 9 ,10]
}