Pure function and data immutability in functional programming approach

[mhaidarhanif]

let names = ["Haidar", "Hanif"];

// Helper function
const addExclamation = text => {
	const transformedText = text + "!!!";
	return transformedText;
};

// Good example
const displayFormatted = array => {
	return array.map(item => {
		return addExclamation(item);
	});
};

// Bad example
const displayFormattedBad = array => {
	for (let index = 0; index < array.length; index++) {
		array[index] += "!!!";
		const element = array[index];
		console.log(element);
	}
};

const resultNames = displayFormatted(names);

// Avoid changing the data directly
// displayFormattedBad(names);

console.log(names);
console.log(resultNames);