There are a few pitfalls though, the expression has to be valid. That is it, now you’ve a working calculator in react! This was the last component talked about above. Then we set the state to the result so that the display gets updated.Ī quick recap, the Display component on the top takes the state.operations to display input and result. If I do not control the precision, here’s what I get… It has very high precision, it doesn’t care how many you’re actually using. There’s only one type of number, unlike other languages. There’s a fundamental issue with the arithmetic in JavaScript. Math.eval() takes string and gives a number. Mathjs has it’s own eval function which only parses mathematical expressions. Instead of tinkering with the potential security issues, we use a package called mathjs. We do not use the global eval function to evaluate this string, it’ll evaluate any JavaScript expression, not just a mathematical one. If anything exists in the array, the string is evaluated with math.eval. We must initialize the state, we do this via a constructor. We use this to store the button presses and diplay values in the display bar. If the same state is used to render multiple parts in the page, all values will be updated when it changes from anywhere in the app. What is the state in React? The state in react refers to the data state in a component. Since input variable has to be modified at every press of a button, we’ll use the state to handle this. We’ll store all the user input in a variable and calculate on entering equal to (=) sign. Our calculator performs addition, subtraction, multiplication and division operations.
I’ll break down the calculator app to individual small chunks. This should start a react welcome page, like one below. Make sure not to have space in your app name, beginners make this mistake frequently.
Install create-react-app with npm install create-react-app -global on a terminal.Ĭreate a new react app with create-react-app react-calculator. If you don’t, install NodeJS (comes with npm) from here. Ĭreate-react-app is where we begin to make sure you have node, npm, create-react-app as usual. Here’s the demo of the app we’ll be creating.
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