How to use CryptoJS package in Postman Flows Evaluate block

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How can we use evaluate block in postman flows to validate the hmac signed payload. I’m using the below code

const crypto = require('crypto'); 
const secret = 'mySecretKey'; 
const payload = request.body; 
console.log(payload);
const receivedHmac = payload;
const data = JSON.stringify(payload); 
const generatedHmac = crypto.createHmac('sha256', secret).update(data).digest('hex');
if (receivedHmac === generatedHmac) { 
    console.log('Payload is valid'); 
    } else {
         console.log('Payload is not valid'); 
    }

This is throwing me an error invalid redefinition of global identifier.