javascript function

Question

I am working on a project and need to implement a function called magic_inc that increments or decrements a given value based on a specific logic. The goal of this function is to apply a custom sequence of increments or decrements to the input value. Here's the sequence:

Answer 1

I'd utilize scientific notation to quickly get the coefficient and the exponent.

Cleanup: truncate the coefficient to an int.

Then just take care of the special cases like 1 -> 0.9 and -0.9 -> -1 otherwise increment/decrement the coefficient.

function magic_inc(value, mode) {
  if (typeof value !== 'number' || value === 0) {
    return 0;
  }

  let [a,b] = value.toExponential().toLowerCase().split("e");
  a = parseInt(a, 10);
  
  if(mode === "inc") a = a===-1 ? -.9 : a+1;
  if(mode === "dec") a = a===1 ? .9 : a-1;
  
  return +`${a}e${b}`;
}

console.log(magic_inc(0.5, 'inc')); // Output: 0.6
console.log(magic_inc(-0.3, 'inc')); // Output: -0.2
console.log(magic_inc(1568.548, 'inc')); // Output: 2000
console.log(magic_inc(17, 'dec')); // Output: 9