Javascript – There was an error in evaluating the Pre-request Script

javascriptjsonpostman

I'm trying to access the response of my POST request in Postman via Post Request Script.

I added this 2 lines, under Pre-request Script

let response = pm.response.json(); 
console.log('JSON Response: ',response );

Then, I opened up my Postman console, before hit Send to make my POST request

I kept getting

There was an error in evaluating the Pre-request Script: TypeError: Cannot read property 'json' of undefined

Do I need to enable anything on Postman?

Best Answer

Pre-request scripts are ran before the request is sent. You do not have a response yet.

Try putting your script under the Tests tab, which is ran after a response is received.

Related Solutions

Javascript – Ajax request returns 200 OK, but an error event is fired instead of success

jQuery.ajax attempts to convert the response body depending on the specified dataType parameter or the Content-Type header sent by the server. If the conversion fails (e.g. if the JSON/XML is invalid), the error callback is fired.

Your AJAX code contains:

dataType: "json"

In this case jQuery:

Evaluates the response as JSON and returns a JavaScript object. […] The JSON data is parsed in a strict manner; any malformed JSON is rejected and a parse error is thrown. […] an empty response is also rejected; the server should return a response of null or {} instead.

Your server-side code returns HTML snippet with 200 OK status. jQuery was expecting valid JSON and therefore fires the error callback complaining about parseerror.

The solution is to remove the dataType parameter from your jQuery code and make the server-side code return:

Content-Type: application/javascript

alert("Record Deleted");

But I would rather suggest returning a JSON response and display the message inside the success callback:

Content-Type: application/json

{"message": "Record deleted"}

Javascript – Why does the JavaScript code receive a “No ‘Access-Control-Allow-Origin’ header is present on the requested resource” error, while Postman does not

If I understood it right you are doing an XMLHttpRequest to a different domain than your page is on. So the browser is blocking it as it usually allows a request in the same origin for security reasons. You need to do something different when you want to do a cross-domain request. A tutorial about how to achieve that is Using CORS.

When you are using Postman they are not restricted by this policy. Quoted from Cross-Origin XMLHttpRequest:

Regular web pages can use the XMLHttpRequest object to send and receive data from remote servers, but they're limited by the same origin policy. Extensions aren't so limited. An extension can talk to remote servers outside of its origin, as long as it first requests cross-origin permissions.

Best Answer

Related Solutions

Javascript – Ajax request returns 200 OK, but an error event is fired instead of success

Javascript – Why does the JavaScript code receive a “No ‘Access-Control-Allow-Origin’ header is present on the requested resource” error, while Postman does not

Related Topic