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importance: 4

Create a calculator that prompts for an arithmetic expression and returns its result.

There’s no need to check the expression for correctness in this task. Just evaluate and return the result.

Run the demo

Let’s use eval to calculate the maths expression:

let expr = prompt("Type an arithmetic expression?", '2*3+2');

alert( eval(expr) );

The user can input any text or code though.

To make things safe, and limit it to arithmetics only, we can check the expr using a regular expression, so that it only may contain digits and operators.