Unleashing the Power of TypeScript/

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Reducer Basics

Reducer Basics

Learn about the workings of a reducer.

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At its most fundamental level, a reducer is simply a function that takes two arguments: the current state and an object representing an action that has occurred. The reducer returns the new state based on that action.

A diagram showing how a reducer works
A diagram showing how a reducer works

Working of reducer

The following code is regular JavaScript, but it could easily be converted to TypeScript by adding any types to state and action:

Javascript (babel-node)
export const incrementAction = { type: 'Increment' };
export const decrementAction = { type: 'Decrement' };
export const counterReducer = (state, action) => {
  if (action.type === 'Increment') {
    return { count: state.count + 1 };
  }
  if (action.type === 'Decrement') {
    return { count: state.count - 1 };
  }
  return state;
};
let state = { count: 1 };
state = counterReducer(state, incrementAction);
state = counterReducer(state, incrementAction);
state = counterReducer(state, decrementAction);
console.log(state); // Logs: { count: 2 }

Let’s explain the code sample above:

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