Extraction Method

Introduction

The extraction method uses to reduce nesting in code. This involves taking a nested code block and extracting it into its own function. This allows you to separate the logic and functionality of the code block, making it easier to understand and maintain.

Tips

Always start extraction from the inner block and then go up.

Example

Write a function that takes an array and return sums of all odd number. It must validate the arguments.

Original nested code:

function sumOdd(numbers) {
  let total = 0;
  if (Array.isArray(numbers)) {
    for (const number of numbers) {
      if (typeof number === "number") {
        if (number % 2 !== 0) {
          total += number;
        }
      }
    }
  }
  return total;
}

Extracted code:

function filterNumber(number) {
  if (number % 2 !== 0) {
    return number;
  }
  return 0;
}

function isValidNumber(number) {
  if (typeof number === "number") {
    return number;
  }
  return 0;
}

function calculateTotal(numbers) {
  let total = 0;
  for (const number of numbers) {
    const validNumber = isValidNumber(number);
    total += filterNumber(validNumber);
  }
  return total;
}

function sumOdd(numbers) {
  let total = 0;
  if (Array.isArray(numbers)) {
    total = calculateTotal(numbers);
  }
  return total;
}