How to distinguish imperative programming style from declarative, and what are their main differences?

The imperative programming style describes how to perform a task, specifying actions and changes of state step by step.

The declarative style describes what needs to be achieved without going into implementation details.

For example, in JavaScript:

// Imperative style
const numbers = [1, 2, 3, 4, 5];
const evens = [];
for (let i = 0; i < numbers.length; i++) {
  if (numbers[i] % 2 === 0) {
    evens.push(numbers[i]);
  }
}

// Declarative style
const evens = numbers.filter(n => n % 2 === 0);

Main differences:

• Imperative code is more detailed and controls the process.
• Declarative code is shorter, easier to read and maintain.
• The declarative style is often used in functional programming and when working with databases (SQL).