Simple JS coding test.

coding-test.js

const users = [{
	name: 'Charlie',
	ranking: 30,
}, {
	name: 'Alice',
	ranking: 10,
}, {
	name: 'Eve',
	ranking: 40,
}, {
	name: 'Bob',
	ranking: 20,
}];

function rank(users) {
	// slice(0) will clone the array to leave the original array untouched.

	return users.slice(0).sort((a, b) => a.ranking > b.ranking);
}

function calculateAvg(users) {
	// Nice, but not performant...

	return users.map(user => user.ranking).reduce((total, value) => total + value, 0) / users.length;
}

function calculateAvgFast(users) {
	// Much better :D

	let i = 0;
	let sum = 0;
	let total = users.length;

	for (;i < total;) {
		sum += users[i].ranking;

		++i;
	}

	return sum / total;
}

// rank() test:

const sorted = rank(users).map(user => user.name).join(', ');
const sortedOk = ["Alice", "Bob", "Charlie", "Eve"].join(', ') === sorted;

console.log(`${ sortedOk ? '✔' : '×' } Sorted: ${ sorted }`);

// avg() test:

let avg = calculateAvg(users);
let avgOk = avg === 25;

console.log(`${ avgOk ? '✔' : '×' } Avg: ${ avg }`);

// calculateAvg() performance:

let t0 = performance.now();
let i = 1000000;

while(--i) {
	calculateAvg(users);
}

console.log(`Took ${ performance.now() - t0 } ms.`);

// calculateAvgFast() test:

avg = calculateAvgFast(users);
avgOk = avg === 25;

console.log(`${ avgOk ? '✔' : '×' } Avg: ${ avg }`);

// calculateAvgFast() performance:

t0 = performance.now();
i = 1000000;

while(--i) {
	calculateAvgFast(users);
}

console.log(`Took ${ performance.now() - t0 } ms.`);