high order function in javascript

high-order-function.js

/*
* Chaining of map() and reduce() function
*/
(function() {
	"use strict"
	const object = [{id: 1, name: "normal object1"}, {id: 2, name: "normal object2"}, {id: 3, name: "normal object3"}]
	const providers = [];

	object.map(mapToProviderObject)
	.reduce(pushFilteredProviders, providers);
	// .reduce((collect, each, index, array) => providers.push(each), providers); // can be use either way

	function mapToProviderObject(provider) {
	    const providerObj = {
	        providerId: provider.id,
	        provider: "mapped => provider Object",
	        name:  " not - " +provider.name
	    };
	    return providerObj;
	}

	function pushFilteredProviders(thisProviderObject, loopProviderObject) {
		// arguments => collectionObject, iteratingObject, index, array
		arguments[0].push(loopProviderObject);
	    return arguments[0];
	}

	console.log(providers);

})();


/*
* Get sum of double even numbers in the list 
*/
(function() {
	"use strict"
	const list = [1, 2, 3, 4, 5, 6, 7, 8, 9];

	const sumOfEves = list
	  .filter(v =>  v % 2 === 0) // filter for even number
	  .map(v => v * 2) // map to double of itself
	  .reduce((sum, element, i, array) => sum + element, 0); // collect and make sum

	console.log("Sum of double of evens are " + sumOfEves);

})();

/*
* removing Object with duplicate properties in List
*/
(function() {
	"use strict"
	const list = [{id: 1}, {id: 2}, {id: 3}, {id: 3}, {id: 4}, {id: 5}, {id: 6}, {id: 7}, {id: 8}];

	console.log("before");
	console.log(list);

	function unlike(collection, key) {
		var items = {}; // temp array, for inserting flags for each item
	    return collection.filter(each => {
	    	var found = items[each[key]]; // fetch from temp array 
	    	items[each[key]] = true; // set flag for item inserted
	    	return !found; // if not found then insert into our collection
	    });
	}

	console.log("after unliking...");
	console.log(unlike(list, 'id'));

})();

/*
* Find greatest number in provided param
*/
(function() {
	"use strict"
	var smallest, biggest;	
	function whichIsGreatest() {
		var great = arguments[0];
		[].forEach.call(arguments, function (el) {
	        el > great ? great = el : '';
	    });
	    return great;
	};

	function otherWay(...args) {
		return args.reduce((greatest, element, i, array) => element > greatest ? greatest = element : greatest, 0);
	}

	console.log(whichIsGreatest(100,2,3,4,5,6,7,8,9));
	console.log(otherWay(100,2,3,4,5,6,7,8,9));

})();

/*
* Non-Mutable javaScript objects
*/
(function() {
	"use strict"
	var mutableObject = {
		id: 1,
		identity: "mutable"
	};

	console.log(mutableObject);
	console.log("try to change the object");

	mutableObject = {
		id: 22,
		identity: "changed"
	};
	
	console.log(mutableObject);

	const partiallyImmutable = {
		id: 2,
		identity: "partially Immutable"
	};

	console.log(partiallyImmutable);
	console.log("try to change the object");

	try{
		partiallyImmutable = {
			id: 22,
			identity: "partially Immutable infected"
		};
	}catch(error) {
		console.log("cannot be changed, its constant");
	}

	console.log("lets try to change it from properties");

	partiallyImmutable.id = 22;
	partiallyImmutable.identity = "partially Immutable infected";

	console.log("it had been changed");
	console.log(partiallyImmutable);

	var mutable = {
		id: 1,
		identity: "fully Immutable"
	};
	const fullyImmutable = Object.freeze(mutable);

	try{
		fullyImmutable.id = 22;
		fullyImmutable.identity = "fully Immutable infected";
	}catch(error) {
		console.log("cannot be changed, fully Immutable object");
	}

})();

/*
* Passing function as param
*/
(function() {
	"use strict"
	function double(el) {  
	    return el + el; 
	};

	function multiplyByItself(el) {
		return el * el;
	};
	
	console.log("double it, then return the multiple of double");
	var fn = double(5); // double it
	console.log(multiplyByItself(fn)); // then return the multiple of double

	console.log("multiple it, then return the double of multiple");
	fn = multiplyByItself(5); // multiple it
	console.log(double(fn)); // then return the double of multiple
	
})();