I created javascript to test Rest APIs to an application from Postman. I am now trying to convert or rewrite it to be used in Salesforce to do the same. I am having a hard time in doing so. Any suggestions?

I created javascript to test Rest APIs to an application from Postman. I am now trying to convert or rewrite it to be used in Salesforce to do the same. I am having a hard time in doing so. Any suggestions?