Modulo Solutions (JS)

mod.js

function modBySubtract(num, modBy) {
	// floor truncates a decimal on a double
	// num/modBy = 20/3 = 6.6667
	// floor(num/modBy) = 6
	// so we're finding the total full count of modBy within num
	// then subtracting to find the remainder
	// will throw a divideByZero runtime error if modBy = 0
	let fullAmountCount = Math.floor(num/modBy)
	return num - modBy*fullAmountCount
}

function modByMod(num, modBy) {
	// equivalent of this in MATLAB
	// mod(num, modBy) - https://www.mathworks.com/help/matlab/ref/mod.html
	return num % modBy
}

function modByLoop(num, modBy) {
	// the reason I don't do any checks if num > 0
	// is that num >= modBy will catch anything
	// and !modBy returns if modBy is a null or 0 value
	// which would cause an infinite loop
	if (!modBy) return num

	while (num >= modBy) {
		num -= modBy
	}

	return num
}

console.log(`modBySubtract: ${modBySubtract(20, 3)}`)
console.log(`modBySubtract: ${modBySubtract(2*Math.PI+Math.PI/6, 2*Math.PI)}`)
// Outputs
// modBySubtract: 2
// modBySubtract: 0.5235987755982991

console.log(`modByMod: ${modByMod(20, 3)}`)
console.log(`modByMod: ${modByMod(2*Math.PI+Math.PI/6, 2*Math.PI)}`)
// Outputs
// modByMod: 2
// modByMod: 0.5235987755982991

console.log(`modByLoop: ${modByLoop(20, 3)}`)
console.log(`modByLoop: ${modByLoop(2*Math.PI+Math.PI/6, 2*Math.PI)}`)
// Outputs
// modByLoop: 2
// modByLoop: 0.5235987755982991