Swapping Two Numbers, but only in a special case

I guess we all know about destructuring to swap two variables a and b, namely: [a, b] = [b, a] and other clever ways like a = b + (b = a, 0). However, I have a different situation which I feel should have a simple answer.

I have a variable a that can be one of 0, 1, 2, 3, 4, 5, or 6. If it is a===3 then I want a to reassign to 4. If a===4 then I want a to reassign to 3. BUT if a is any of the other values, I want it to remain the same.

So is there a clever, 1 line bit of code that can do this? For completeness, I want a short version of this:

switch(a){
    case 3: a = 4; break;
    case 4: a = 3; break;
    // default: a = a; break; // Hashed out, because it is not needed
}

>Solution :

Using a Computed Property Name

function test(a) {
  a = { [a]: a, 3: 4, 4: 3 }[a]; 
  return a;
}


[0, 1, 2, 3, 4, 5].forEach(n =>console.log(n, test(n)));