Postman – Parsing HTML responses

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I recently did a blog post on sharing and comparing values in XML and JSON payloads after getting some questions around the topic. Another common question I get in my training sessions that are similar to parsing payloads is around parsing HTML so that you can store values or assert on them for checking purposes, so again I thought I would share my solution on how you can parse an HTML response.

The problem

Let’s say we have a web page like the one below that we are running checks against:

Parsing HTML response - a screenshot of w3schools list page

What if we wanted to check, say for example, that the correct text was added to the first and second items of the ordered list? When HTML is retrieved by Postman it’s stored as a string in a variable named responseBody meaning we could do a string comparison asserting that the sub-string ‘First item’ and ‘Second item’ exist in responseBody. However, this is a very simplistic way of asserting with little flexibility. What if there was more than one ‘First item’ or ‘Second item’ on the page, what if you wanted to get the values from those items to use in a future request?

Parsing HTML payloads

Firstly, click here to download the Postman collection to access the requests and tests. You will find a single request that requests the page then runs a couple of checks. So let’s take a look at the code in the Test tab:

1. Native JavaScript solution

GET www.w3schools.com/html/html_lists.asp

var responseHTML = document.createElement("html");
responseHTML.innerHTML = responseBody;

inputs = responseHTML.querySelector(".w3col > ol > li:nth-child(1)");

tests["First item in list is named 'First item'"] = inputs.innerHTML === "First item";

Let’s review this test code:
1. Since Postman uses JavaScript we can build DOM (Document object model) on the fly by calling document.createElement("html") and then adding the responseBody into the DOM to fill it with the HTML under tests
2. We can use the method querySelector to execute a CSS locator search for the first list item we want to assert against

2. JQuery solution

The first solution uses native JavaScript functions but you Postman also supports jQuery and you can use it to achieve the same outcome as the native JavaScript approach.

GET www.w3schools.com/html/html_lists.asp

var html = $.parseHTML(responseBody); 
var jqResponseHTML = $(html);
result = jqResponseHTML.find('.w3col > ol > li:nth-child(2)');

tests["First item in list is named 'Second item'"] = result[0].innerHTML == "Second item";

Let’s review this test code:
1. We use parseHTML() to convert the responseBody string into a DOM and then call $(html) to allow us to access jQuery functions
2. The jQuery function find() allows us to do a CSS locator search for the second list item we want to assert against

Conclusion

The above examples show that parsing HTML by using either approach results in a quick and easy way to create a searchable DOM based on your requested HTML with all the standard JavaScript and/or jQuery methods you need to assert and store information from your original request.

References

  1. W3Schools – http://www.w3schools.com
  2. JavaScript API – https://developer.mozilla.org
  3. jQuery API – https://api.jquery.com

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