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Redux Calculator

Setup

To begin, fork and clone this repository. Once it has finished downloading cd into the project root and run npm i to fetch the project dependencies. After they are fetched run npm start and a browser window will open at http://localhost:3000 displaying a (non-functioning) calculator app. In another terminal window run npm test to run the test suite.

The Plan

This project's goal is to recreate the standard OSX calculator in React, handling all state changes in Redux. A layout is provided, but none of the functionality is implemented yet.

Step 1

Summary

Our first step will be installing the necessary dependencies and connecting our application to Redux. Before beginning, take a few minutes get familiar with the provided components. The root component, Calculator serves primarily as a container component, passing props to its children. The Display component is a functional component that simply renders some markup and will display the calculator's value. The CalculatorButton component is another functional component, and will be the user's primary point of interaction with the application.

Instructions

  • Install Redux and React-Redux
  • Create an initial state and reducer function in src/ducks/calculator.js
  • Create a store in src/store.js
  • Make the React application aware of Redux using the Provider component
  • Connect the Calculator component definition to the Redux store

Detailed Instructions

Start out by running npm i redux react-redux --save to download our dependencies and save them to the package.json. Open src/ducks/calculator.js and create an initialState variable. initialState should be an object with three properties:

  • currentValue - Set equal to "0" (note that it is a string!). This is where we will be storing the calculator's current value that displays on screen.
  • operator - Set equal to null. This will be a string representation of what operation the user wants to use, i.e "DIVIDE" or "MULTIPLY"
  • previousValue - Set equal to 0 (not a string!). This is the value that the user entered before selecting an operation.

Beneath initialState we'll create the reducer function. Create and export by default a function named calculator which takes two parameters:

  • state, which defaults to initialState. An object representation of the application's current state.
  • action, an object describing what has prompted the state change.

For now, calculator should simply return state.

We can now use this reducer to create our Redux store. Open up src/store.js and import createStore from Redux and our calculator reducer. Create the store by invoking createStore and passing calculator as an argument. Export the result of this invocation by default. Remember that this store is just a plain JavaScript object containing all of our state data.

Next we will make our React application aware of the store using the Provider component. In src/index.js import Provider from React-Redux and store from src/store.js. Wrap the root component (Calculator) in the Provider component, passing store as a prop to Provider.

Now that our application overall knows about our Redux store, we need to connect a component and actually access that data. In src/components/Calculator.js import connect from React-Redux. Underneath Calculator's component definition create a function named mapStateToProps. This function takes a single parameter, state, and simply returns state.

mapStateToProps is how we tell Redux which pieces of state this component is interested in. Right now our application state is small and focused on this one component, but in a larger application you might have dozens or hundreds of properties on state! You wouldn't want to pass everything going on in your application to every component! If we wanted to pass only specific properties to a component, our function would look more like this:

`mapStateToProps` specific properties example: 
function mapStateToProps( state ) {
	return { currentValue: state.currentValue };
}

In the above example we would have access to this.props.currentValue inside the component, but not previousValue or operator.

Once mapStateToProps is completed we can use it in conjunction with connect to decorate the Calculator component definition. Create the decorator by invoking connect and passing mapStateToProps as an argument, then decorate your component definition by invoking the decorator and passing in Calculator. Export the decorated component definition by default. This pattern takes some getting used to, so here's a reminder:

Decorator Example 
function mapStateToProps( state ) {
	return state;
}
const decorator = connect( mapStateToProps );
const decoratedComponent = decorator( App );
export default decoratedComponent;

This is usually shortened to

function mapStateToProps( state ) {
	return state;
}
export default connect( mapStateToProps )( App );

You should now be able to console.log( this.props ) inside of Calculator's render method and see an object containing state information.

**Code Solution**
`src/ducks/calculator.js` 
const initialState = {
	  currentValue: "0"
	, operator: null
	, previousValue: 0
};

export default function calculator( state = initialState, action ) {
	return state;
}
`src/store.js` 
import { createStore } from "redux";

import calculator from "./ducks/calculator";

export default createStore( calculator );
`src/index.js` 
import React from "react";
import ReactDOM from "react-dom";
import { Provider } from "react-redux";

import "./index.css";

import store from "./store";

import Calculator from "./components/Calculator";

ReactDOM.render(
	<Provider store={ store }>
		<Calculator />
	</Provider>,
	document.getElementById( 'root' )
);
`src/components/Calculator.js` 
import React, { Component } from "react";
import { connect } from "react-redux";

import "./Calculator.css";

import CalculatorButton from "./CalculatorButton/CalculatorButton";
import Display from "./Display/Display";

export class Calculator extends Component {
	/* Calculator definition */
}

function mapStateToProps( state ) {
	return state;
}

export default connect( mapStateToProps )( Calculator );

Step 2

Summary

In this step we will begin adding some basic functionality to the calculator through Redux actions.

Instructions

  • Create the ENTER_NUMBER, CLEAR, PERCENTAGE, and TOGGLE_NEGATIVE action types, and their corresponding action creators
  • Place the action creators onto Calculator's props via connect
  • Assign the action creator functions to the appropriate JSX elements
  • Update Display to display currentValue
  • Update CalculatorButton to call the functions on click

Detailed Instructions

We'll start this step in src/ducks/calculator.js. At the top of the file create the four following action types, set equal to string values of their variable name:

  • ENTER_NUMBER - "ENTER_NUMBER"
  • CLEAR - "CLEAR"
  • PERCENTAGE - "PERCENTAGE"
  • TOGGLE_NEGATIVE - "TOGGLE_NEGATIVE"

Below the reducer, create action creators for each of these action types. The clear, percentage, and toggleNegative action creator functions should simply return an object with the appropriate type property. enterNumber will take a single parameter number and return an object with a type of ENTER_NUMBER and the number parameter. Export all of these action creators.

Now we need to refactor the calculator reducer to handle these actions. Remember that currentValue is a string, this will make some parts easier and other parts a bit more difficult.

Begin by writing a switch statement that checks action.type with a default case that returns state. The first case we will check for (make sure it is above default!) will be ENTER_NUMBER. In the case of ENTER_NUMBER we will use Object.assign to return a copy of state where currentValue is changed to include action.number. There are a few gotcha's here:

  • What if currentValue is at its default of "0"? We don't want our calculator to display "04".
  • Remember that we want currentValue to stay as a string, don't forget to convert the action.number to a string
The `ENTER_NUMBER` case should look something like this: 
return Object.assign( {}, state, {
	// If state.currentValue is at its default, simply replace it with the given number
	// Otherwise, concatenate the strings
	currentValue: state.currentValue === "0" ? action.number.toString() : state.currentValue + action.number.toString()
} );

Next up is an easy one - the CLEAR case. When passed an action of type CLEAR the reducer should simply return initialState, resetting to its default values.

After clear comes the PERCENTAGE case. When passed an action of type PERCENTAGE the reducer should return a copy of state wherecurrentValue has been divided by 100. To do this you will need to convert curentValue to a number, divide it by 100, and then convert it back to a string. Keep in mind that the number could be a decimal, so parseInt may not work!

The last action in this step is TOGGLE_NEGATIVE. This case should return a copy of state where currentValue has been converted from positive to negative (or vice-versa). This can be achieved like this: ( -parseFloat( state.currentValue ) ).toString().

Our reducer is able to handle these actions, so let's put them to work. Open up src/components/Calculator.js and import the four newly made action creators. We need these action creators wrapped in Redux's dispatch function and added to Calculator's props, so we'll have to update our connect decorator. Pass an object consisting of the action creators as a second argument to connect.

Inside of Calculate's render method destructure currentValue, enterNumber, clear, percentage and toggleNegative from this.props. Pass currentValue to the Display component's value prop. In the map where the numberButtons are created change the callback prop so that it invokes enterNumber passing in the current number, like so: callback={ () => enterNumber( number ) }. Pass clear, percentage, and toggleNegative to the callback prop of the appropriate buttons. Finally, use enterNumber in the decimal button, passing in "." as an argument.

Open up src/components/Display/Display.js and alter the JSX so that it displays its value prop instead of a static 0. Open src/components/CalculatorButton/CalculatorButton.js and give the top level <button> element an onClick prop, passing in callback.

You should now be able to enter values, see them appear in the display, reset the display to 0, toggle the value between positive and negative, and divide the value by 100 using the percentage button.

**Code Solution**
`src/ducks/calculator.js` 
const CLEAR = "CLEAR";
const ENTER_NUMBER = "ENTER_NUMBER";
const PERCENTAGE = "PERCENTAGE";
const TOGGLE_NEGATIVE = "TOGGLE_NEGATIVE";

const initialState = {
	  currentValue: "0"
	, operator: null
	, previousValue: 0
};

export default function calculator( state = initialState, action ) {
	switch ( action.type ) {
		case ENTER_NUMBER:
			return Object.assign(
				  {}
				, state
				, { currentValue: state.currentValue === "0" ? action.number.toString() : state.currentValue + action.number.toString() }
			);
		case PERCENTAGE:
			return Object.assign( {}, state, { currentValue: ( parseFloat( state.currentValue ) / 100 ).toString() } );
		case CLEAR:
			return {
				  currentValue: "0"
				, operator: null
				, previousValue: 0
			};
		case TOGGLE_NEGATIVE:
			return Object.assign( {}, state, { currentValue: ( -parseFloat( state.currentValue ) ).toString() } );
		default:
			return state;
	}
}

export function clear() {
	return { type: CLEAR };
}

export function enterNumber( number ) {
	return { number, type: ENTER_NUMBER };
}

export function percentage() {
	return { type: PERCENTAGE };
}

export function toggleNegative() {
	return { type: TOGGLE_NEGATIVE };
}
`src/components/Calculator.js` 
import React, { Component } from "react";
import { connect } from "react-redux";

import "./Calculator.css";

import { operators } from "../operators";
import {
	  enterNumber
	, percentage
	, clear
	, toggleNegative
} from "../ducks/calculator";

import CalculatorButton from "./CalculatorButton/CalculatorButton";
import Display from "./Display/Display";

export class Calculator extends Component {
	render() {
		const {
			  currentValue
			, enterNumber
			, percentage
			, clear
			, toggleNegative
		} = this.props;
		const numberButtons = [ 7, 8, 9, 4, 5, 6, 1, 2, 3, 0 ].map( number => (
			<CalculatorButton
				callback={ () => enterNumber( number ) }
				key={ number }
				value={ number }
				wide={ number === 0 }
			/>
		) );

		return (
			<main className="calculator">
				<Display value={ currentValue } />
				<div className="calculator__buttons-wrapper">
					<section className="calculator__left-buttons">
						<CalculatorButton
							backgroundColor="#d6d6d6"
							callback={ clear }
							value="AC"
						/>
						<CalculatorButton
							backgroundColor="#d6d6d6"
							callback={ toggleNegative }
							value="+/-"
						/>
						<CalculatorButton
							backgroundColor="#d6d6d6"
							callback={ percentage }
							value="%"
						/>
						{ numberButtons }
						<CalculatorButton
							callback={ () => enterNumber( "." ) }
							value="."
						/>
					</section>
					<section className="calculator__operator-buttons">
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => null }
							color="#ffffff"
							value="÷"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => null }
							color="#ffffff"
							value="×"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => null }
							color="#ffffff"
							value="-"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => null }
							color="#ffffff"
							value="+"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => null}
							color="#ffffff"
							value="="
						/>
					</section>
				</div>
			</main>
		);
	}
}

function mapStateToProps( state ) {
	return state;
}

export default connect( mapStateToProps, {
	  clear
	, enterNumber
	, percentage
	, toggleNegative
} )( Calculator );
`src/components/Display/Display.js` 
import React from "react";

import "./Display.css";

export default function Display( { value } ) {
	return (
		<div className="display">
			<div className="display__window-button-wrapper">
				<div className="display__window-button" />
				<div className="display__window-button" />
				<div className="display__window-button" />
			</div>
			{ value }
		</div>
	);
}
`src/components/CalculatorButton/CalculatorButton.js` 
import React, { PropTypes } from "react";

import "./CalculatorButton.css";

export default function CalculatorButton( { backgroundColor, callback, color, value, wide } ) {
	return (
		<button
			onClick={ callback }
			className={ `calculator-button${ wide ? " calculator-button--wide" : "" }` }
			style={ { backgroundColor, color } }
		>
			{ value }
		</button>
	);
}

CalculatorButton.propTypes = {
	  backgroundColor: PropTypes.string
	, callback: PropTypes.func
	, color: PropTypes.string
	, wide: PropTypes.bool
};

CalculatorButton.defaultProps = {
	  backgroundColor: "#e0e0e0"
	, color: "black"
	, wide: false
};

Step 3

Summary

In this step we will implement the functionality to handle mathematical operations.

Instructions

  • Create EVALUATE and SET_OPERATOR action types and their corresponding action creators
  • Create a calculate function in src/calculate.js
  • Refactor the calculator reducer to make use of calculate and handle the new actions
  • Map the new action creators to the Calculator component definition's props
  • Assign the action creators to the appropriate JSX elements

Detailed Instructions

Begin this step in src/ducks/calculator.js. Create two new action types - EVALUATE and SET_OPERATORas well as corresponding action creators. The evaluate action creator should simply return an object with a type of EVAlUATE, the setOperator action creator should take a parameter of operator and return an object with the type SET_OPERATOR and the operator.

Now that our action creators are finished, we need to find a way to actually calculate these operations. Open up src/calculate.js and create the function calculate. calculate should be exported and take three parameters - currentValue, previousValue and operator. Because the operator we are storing on state is a string, we need to check what type of operator we are working with before calculating the result. To do this we'll need import the provided operators object from src/operators.js. The operators object is just a list of constants that looks like this:

export const operators = {
	  ADD: "ADD"
	, DIVIDE: "DIVIDE"
	, MULTIPLY: "MULTIPLY"
	, SUBTRACT: "SUBTRACT"
};

The reason we store them this way is to avoid "magic strings". Hard coding the string into multiple places comes with a lot of downsides, such as potential for typos, needing to find and change all of them if the string is ever changed, and confusion from developers later reading the code.

Now that we have our object full of operators, let's add a switch statement to the calculate function that checks the operator parameter. Add a case for each of the possible operators that returns the value of the necessary calculation (i.e case operators.DIVIDE: return previousValue / currentValue). For safety, add a default case that simply returns currentValue.

Import the calculate function to src/ducks/calculator.js. Add a case to the reducer that handles EVALUATE actions. This case should return an object where operator and previousValue are returned to their initial values, and currentValue is set equal to the result of the calculate function. A few notes for currentValue:

  • state.currentValue is a string, and `calculate will be expecting a number
  • We want the updated currentValue to be a string as well, don't forget to convert the result of calculate

We now need to add a case for handling the SET_OPERATOR action type. This case should return an object where currentValue is set to "0", and operator is set to action.operator. previousValue will be a little tricky. To know what to set previousValue to, we first have to check whether or not there is already on operator on state. If there is not an operator on state, we can simply set previousValue equal to state.currentValue, if there is already an operator on state then we need to set previousValue equal to the result of the calculate function. It will look something like this: previousValue: state.operator ? calculate( parseFloat( state.currentValue ), state.previousValue, state.operator ) : parseFloat( state.currentValue ).

Let's go put these action creators to use in src/components/Calculator.js! Import the two new action creators as well as the operators object. Add these action creators to the object passed as the second argument to connect. Pass the evaluate action creator to the callback prop on the = button. Change the callback prop for the +, -, ÷, and × buttons so that it invokes setOperator, passing the appropriate operator from the operators object.

You should now have a functioning calculator capable of the same basic functionality as your computer's calculator!

**Code Solution**
`src/ducks/calculator.js` 
import { calculate } from "../calculate";

const CLEAR = "CLEAR";
const ENTER_NUMBER = "ENTER_NUMBER";
const EVALUATE = "EVALUATE";
const PERCENTAGE = "PERCENTAGE";
const SET_OPERATOR = "SET_OPERATOR";
const TOGGLE_NEGATIVE = "TOGGLE_NEGATIVE";

const initialState = {
	  currentValue: "0"
	, operator: null
	, previousValue: 0
};

export default function calculator( state = initialState, action ) {
	switch ( action.type ) {
		case ENTER_NUMBER:
			return Object.assign(
				  {}
				, state
				, {
					currentValue: state.currentValue === "0" ? action.number.toString() : state.currentValue + action.number.toString()
				}
			);
		case SET_OPERATOR:
			return {
				  currentValue: "0"
				, operator: action.operator
				, previousValue: state.operator ? calculate( parseFloat( state.currentValue ), state.previousValue, state.operator ) : parseFloat( state.currentValue )
			};
		case PERCENTAGE:
			return Object.assign( {}, state, { currentValue: ( parseFloat( state.currentValue ) / 100 ).toString() } );
		case CLEAR:
			return {
				  currentValue: "0"
				, operator: null
				, previousValue: 0
			};
		case EVALUATE:
			return {
				  currentValue: calculate( parseFloat( state.currentValue ), state.previousValue, state.operator ).toString()
				, operator: null
				, previousValue: 0
			};
		case TOGGLE_NEGATIVE:
			return Object.assign( {}, state, { currentValue: ( -parseFloat( state.currentValue ) ).toString() } );
		default:
			return state;
	}
}

export function clear() {
	return { type: CLEAR };
}

export function enterNumber( number ) {
	return { number, type: ENTER_NUMBER };
}

export function evaluate() {
	return { type: EVALUATE };
}

export function percentage() {
	return { type: PERCENTAGE };
}

export function setOperator( operator ) {
	return { operator, type: SET_OPERATOR };
}

export function toggleNegative() {
	return { type: TOGGLE_NEGATIVE };
}
`src/calculate.js` 
import { operators } from "./operators";

export function calculate( currentValue, previousValue, operator ) {
	switch ( operator ) {
		case operators.ADD:
			return previousValue + currentValue;
		case operators.DIVIDE:
			return previousValue / currentValue;
		case operators.MULTIPLY:
			return previousValue * currentValue;
		case operators.SUBTRACT:
			return previousValue - currentValue;
		default:
			return currentValue;
	}
}
`src/components/Calculator.js` 
import React, { Component } from "react";
import { connect } from "react-redux";

import "./Calculator.css";

import { operators } from "../operators";
import {
	  enterNumber
	, setOperator
	, percentage
	, clear
	, evaluate
	, toggleNegative
} from "../ducks/calculator";

import CalculatorButton from "./CalculatorButton/CalculatorButton";
import Display from "./Display/Display";

export class Calculator extends Component {
	render() {
		const {
			  currentValue
			, enterNumber
			, setOperator
			, percentage
			, clear
			, evaluate
			, toggleNegative
		} = this.props;
		const numberButtons = [ 7, 8, 9, 4, 5, 6, 1, 2, 3, 0 ].map( ( number ) => (
			<CalculatorButton
				callback={ () => enterNumber( number ) }
				key={ number }
				value={ number }
				wide={ number === 0 }
			/>
		) );

		return (
			<main className="calculator">
				<Display value={ currentValue } />
				<div className="calculator__buttons-wrapper">
					<section className="calculator__left-buttons">
						<CalculatorButton
							backgroundColor="#d6d6d6"
							callback={ clear }
							value="AC"
						/>
						<CalculatorButton
							backgroundColor="#d6d6d6"
							callback={ toggleNegative }
							value="+/-"
						/>
						<CalculatorButton
							backgroundColor="#d6d6d6"
							callback={ percentage }
							value="%"
						/>
						{ numberButtons }
						<CalculatorButton
							callback={ () => enterNumber( "." ) }
							value="."
						/>
					</section>
					<section className="calculator__operator-buttons">
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => setOperator( operators.DIVIDE ) }
							color="#ffffff"
							value="÷"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => setOperator( operators.MULTIPLY ) }
							color="#ffffff"
							value="×"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => setOperator( operators.SUBTRACT ) }
							color="#ffffff"
							value="-"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ () => setOperator( operators.ADD ) }
							color="#ffffff"
							value="+"
						/>
						<CalculatorButton
							backgroundColor="#f5923e"
							callback={ evaluate }
							color="#ffffff"
							value="="
						/>
					</section>
				</div>
			</main>
		);
	}
}

function mapStateToProps( state ) {
	return state;
}

export default connect( mapStateToProps, {
	  enterNumber
	, setOperator
	, percentage
	, clear
	, evaluate
	, toggleNegative
} )( Calculator );

Contributions

Contributions

If you see a problem or a typo, please fork, make the necessary changes, and create a pull request so we can review your changes and merge them into the master repo and branch.

Copyright

Copyright

© DevMountain LLC, 2017. Unauthorized use and/or duplication of this material without express and written permission from DevMountain, LLC is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to DevMountain with appropriate and specific direction to the original content.