ReferenceError: fetch is not defined - Postman

Question

In Postman, I run an arbitrary request. I put the following code in either the Pre-req. script or in the Tests script:

fetch('https://jsonplaceholder.typicode.com/todos/3')
  .then(response => response.text())
  .then(responseBody => {
    console.log('The response body:');
    console.log(responseBody);
  });

When I hit the Send button to run the request, I get ReferenceError: fetch is not defined:

When searching online, I have hardly found anything about this error message in Postman. Now, Postman is not a web browser in the normal sense, but just about every well known web browser offers the Fetch API these days.

Does Postman not implement the Fetch API?

Answer 1

Does Postman not implement the Fetch API?

I think not. The closest correspondence to the fetch() command is pm.sendRequest().
But pm.sendRequest returns a pm object and not a Promise, at least for now.

I have found a workaround, though. In the code snippet below I define the pmFetch() function which is meant to do what the fetch() command does in a normal web browser.

pmFetch('https://jsonplaceholder.typicode.com/todos/3')
  .then(response => response.json())
  .then(responseBody => {
    console.log('The response body:');
    console.log(responseBody);
    console.log('responseBody.title: "' + responseBody.title + '"');
  });
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - //
function pmFetch (url) {
  return new Promise ((resolve, reject) => {
    pm.sendRequest(url, function (err, response) {
      if (err) reject(err);
      resolve(response);
    });
  });
}

Here is a link to the Postman Collection in case you want to download, import, and run the collection.

Reference:

• How to make pm.sendRequest return a Promise