What is the difference between procedural and functional programming?

Question

Programming

As a typical "dinosaur", I thought about the question of what is the difference between the two programming styles. From my dinosaur point of view, it's the same thing.
Or are there any such differences?

Answer 1

Example in JavaScript context:
Procedural style:

const array = ['first', 'second'];

let output;

function allOdd(words) {
  let result = true;

  for (let i = 0; i < words.length; ++i) {
    const len = words[i].length;

    if (len % 2 !== 0) {
      result = false;
      break;
    }
  }

  return result;
}

output = allOdd(array);

alert(output);

Functional Style:

function length(string) {
  return prop('length', string);
}

function odd(number) {
  return equals(modulus(number, 2), 0); 
}

function allOdd(...words) {
  return every(compose(odd, length), words);
}

alert(allOdd('first', 'second'));

The implementations of prop , modulus , equals , every and compose are left out. I think it's easy to understand from their name what result they return.

Answer 2

FP does not imply mutable state.
Procedures change some general state.

Answer 3

In declarative programming, you make it clear: I want the factorial of n to be n times the factorial of n-1 (as in the definition of factorial in mathematics). Declarative is what.

const factorial = (n) => {
  return (n === 0) ? 1 : n * factorial(n-1);
}

In imperative , you order to move clearly in steps - multiply this by this while the countdown is on and some numbers are remembered.

const factorial = (n) => {
  const iter = (counter, acc) => {
    return (counter === 0) ? acc : iter(counter - 1, counter * acc);
  }
  return iter (n, 1);
}

Imperative is like.