# Prefix calculator using stack in JavaScript

JavascriptWeb DevelopmentFront End TechnologyObject Oriented Programming

We are required to make a calculator with the RPN (reverse polish notation) input method using Stacks in JavaScript.

Consider the following input array −

const arr = [1, 5, '+', 6, 3, '-', '/', 7, '*'];

Process −

• 1 is an operand, push to Stack.

• 5 is an operand, push to Stack.

• '+' is an operator, pop 1 and 5, calculate them and push result to Stack.

• 6 is an operand, push to Stack.

• 3 is an operand, push to Stack.

• '−' is an operator, pop 6 and 3, subtract them and push result to Stack.

• '/' is an operator, pop 6 and 3, divided them and push result to Stack.

• 7 is an operand, push to Stack.

• '*' is an operator, pop 2 and 7, multiply them and push result to Stack.

And finally, the output should be −

const output = 14;

## Example

The code for this will be −

const arr = [1, 5, '+', 6, 3, '−', '/', 7, '*'];
const stackCalculator = (arr = []) => {
const options = {
'+': (a, b) => a + b,
'−': (a, b) => a - b,
'*': (a, b) => a * b,
'/': (a, b) => a / b
};
const stack = [];
arr.forEach(value => {
stack.push(value in options
? options[value](...stack.splice(-2))
: value
);
});
return stack;
};
console.log(stackCalculator(arr));

## Output

And the output in the console will be −