Class as a set of methods in OOP in JavaScript

Sometimes classes are used to group methods of similar topics. In this case, as a rule, only one object of this class is created and its methods are used many times in different situations.

Let's look at an example. Let's make a class that will manipulate arrays of numbers:

class ArrHelper {
	
}

Each method of this class will take an array as a parameter and perform a given operation on it. Let's say, for example, we have the following methods:

class ArrHelper {
	getSum(arr) {
		// sum of elements
	}
	
	getAvg(arr) {
		// arithmetic mean arithmetical mean mean
	}
}

Let's write the implementation of these methods:

class ArrHelper {
	getSum(arr) {
		let res = 0;
		
		for (let num of arr) {
			res += num;
		}
		
		return res;
	}
	
	getAvg(arr) {
		if (arr.length > 0) {
			let sum = this.getSum(arr);
			return sum / arr.length;
		} else {
			return 0;
		}
	}
}

Let's see how we will use these methods. Let's create an object of our class:

let arrHelper = new ArrHelper;

Let's find the sum of numbers in different arrays using our object:

let sum1 = arrHelper.getSum([1, 2, 3]);
console.log(sum1);

let sum2 = arrHelper.getSum([3, 4, 5]);
console.log(sum2);

Make a class Validator that will check strings for correctness.

Make a method isEmail in your class that checks if a string is a valid email.

Make a method isDomain in your class that checks whether a string is a valid domain name.

Create a method isNumber in your class that checks if a string contains only numbers.