The Factory pattern

Learn the pattern that moves object creation into a factory function.

The Factory pattern

The Factory pattern moves object creation logic into a separate factory function. The calling code does not know which object is produced; it just passes a parameter and gets a result.

This makes code more flexible. To add a new object type you change only the factory; callers stay the same.

Writing a function that produces objects instead of using a class is common in JS.

Factory function example

The factory below produces button objects based on the type parameter. The caller just writes createButton('primary', 'Save'); production details stay inside the factory.

function createButton(type, label) {
  return { label: label, kind: type };
}

This pattern is especially useful when there are many similar object types.

Exercise createButton factory

Write a factory function createButton(type, label). The returned object should have a label property equal to label and a render() method that returns label. If type is 'primary', set button.kind = 'primary'. Finally return the button object.

Show example solution

label, render() { return label; } }, if type is 'primary' set button.kind = 'primary', finally return button.
Example solution:
function createButton(type, label) {
  const button = {
    label: label,
    render() {
      return label;
    }
  };
  if (type === 'primary') {
    button.kind = 'primary';
  }
  return button;
}

Test yourself

What advantage does the Factory pattern provide?
- Sort objects faster
- Auto-clean memory
- Separate object creation from the caller
- Inherit classes
Show answer

Separate object creation from the caller — Correct! Factory moves creation logic into a factory function.

Complete the factory return

function createButton(label) {
  return { label: label, ____() { return label; } };
}

Show answer

function createButton(label) {
  return { label: label, render() { return label; } };
}

Match the Factory concepts

Factory

Separates object creation
createButton()

Factory function
type parameter

Decides which type to make
return {}

Returns a new object

Next lesson: The Observer pattern

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