Javascript find max number from 3 inputs

I've just began Javascript in college. One task is to define and call a function to find the maximum number from 3 numbers entered by the user. I know there is a max() function but we were told to do it manually using if and else if.

I'm going wrong somewhere as you can see. It's just telling me the max is 0 everytime.

function maxNum(num1, num2, num3){
        var max = 0;
        if(num1 > num2){
            if(num1 > num3){
                num1 = max;
            }
            else{
                num3 = max;
            }
        }
        else{
            if(num2 > num3){
                num2 = max;
            }
        }
    return max;
    }

    for(i=0;i<3;i++){
        parseInt(prompt("Enter a number"));
    }
    document.write(maxNum());

Solution 1:

Or you can use ES6 syntax, to compute largest of three numbers in easier way,

const largest = a => F = b => G = c => ((a > b && a > c) ? a : (b > a && b > c) ? b : c)

console.time()
console.log(largest(53)(30907)(23333))
console.timeEnd()

Solution 2:

easiest way:

function maxNum(num1, num2, num3){
    var tmp = 0;
    if(num1 < num2 && num3 < num2) {
        tmp = num2;
    } else if(num3 < num1){
        tmp = num1;
    } else {
        tmp = num3;    
    }
    return tmp;
}
var arr = [];
for(var i = 0; i < 3; i++) {
    arr[i] = prompt("Enter a number");
}
console.log(maxNum.apply(this, arr));