The correct way to do it is to load a 500mb library that has an add function in it.

It's much better to make your own function that uses bitwise operations to do addition.

function add(a, b) {
    while (b !== 0) {
        // Calculate carry
        let carry = a & b;

        // Sum without carry
        a = a ^ b;

        // Shift carry to the left
        b = carry << 1;
    }
    return a;
}

(For certain definitions of better.)

The native arithmetic operators are prone to floating point rounding errors