Modulo and Division Operator

mod-div.js

function mod(x1, x2) {
    if (Math.floor(x1) !== x1 || Math.floor(x2) !== x2) { throw new Error("no floats, please :)"); }

    while (x1 >= x2) {
        x1 -= x2;
    }

    return x1;
}

function div(x1, x2) {
    if (Math.floor(x1) !== x1 || Math.floor(x2) !== x2) { throw new Error("no floats, please :)"); }
    let counter = 0;

    while (x1 >= x2) {
        counter += 1;
        x1 -= x2;
    }

    return counter;
}

// TESTS

console.log("|| MOD ||");
console.log(mod(10, 2) === 0, mod(10, 2), '===', 0);
console.log(mod(11, 2) === 1, mod(11, 2), '===', 1);
console.log(mod(0, 2) === 0, mod(0, 2), '===', 0);
console.log(mod(10, 3) === 1, mod(10, 3), '===', 1);
console.log(mod(11, 3) === 2, mod(11, 3), '===', 2);
console.log(mod(12, 3) === 0, mod(12, 3), '===', 0);
console.log(mod(50, 26) === 24, mod(50, 26), '===', 24);

try {
    mod(10.5, 2);
    console.log("error not working");
} catch (e) {
    console.log("error working");
}

console.log("\n|| DIV ||");
console.log(div(10, 2) === 5, div(10, 2), '===', 5);
console.log(div(11, 2) === 5, div(11, 2), '===', 5);
console.log(div(0, 2) === 0, div(0, 2), '===', 0);
console.log(div(10, 3) === 3, div(10, 3), '===', 3);
console.log(div(11, 3) === 3, div(11, 3), '===', 3);
console.log(div(12, 3) === 4, div(12, 3), '===', 4);
console.log(div(50, 26) === 1, div(50, 26), '===', 1);

try {
    div(10, 2.2);
    console.log("error not working");
} catch (e) {
    console.log("error working");
}

// run in node using `node mod-div.js` or paste into browser console