What is code minification and why does a build tool perform it automatically?

Minification removes unnecessary spaces, comments, and shortens variable names in the final JavaScript file, without changing what the code actually does. This makes the file much smaller so it downloads faster for people visiting the website, especially on slower internet connections.

// Before minification
function addNumbers(firstNumber, secondNumber) {
  return firstNumber + secondNumber;
}

// After minification
function a(b,c){return b+c}