How to Write Scripts in Postman

Let’s briefly go through the basics of writing code in JavaScript.

1. Variables

A variable is a container for storing information. The keyword var is used to declare a variable.

var name = "Astronaut cat";

var age = 4;

var isReadyForLaunch = true;

var inventory = ["helmet", "gloves", "rations"];

2. Functions

Functions are created using the keyword function.

Let’s assume we have two functions: one prepares the ship for launch, the other calculates the fuel reserve.

function prepareShip(name) {
    return "The ship «" + name + "» is ready for launch!";
}

function calculateFuel(distance) {
    return distance * 42;
}

3. Calling Functions

Functions are called by name and can accept arguments. Let’s see how this looks in code.

prepareShip("Voskhod-3");

var fuel = calculateFuel(800);

console.log("Launch has started!");

Postman provides an execution environment where you can write JavaScript scripts — the so-called “Postman Sandbox”. You can write code in the section Scripts.

You can call Postman’s special functions by accessing the methods and properties of the object named pm.

1. pm.environment

Using the pm object, you can access the environment property and dynamically get and set environment variables.

pm.environment.get("variableName")

pm.environment.set("variableName", "variableValue")

2. pm.globals

Using the pm object, you can access the globals property and work dynamically with global variables (available across all environments).

pm.globals.get("variableName")

pm.globals.set("variableName", "variableValue")

3. pm.test

Using the pm object, you can call the test method to write your own test.

pm.test("Let's check if code is 200",
    function () {
        pm.response.to.have.status(200);
    }
);

Scripts defined in the Scripts —> Pre-request section are executed before a request is sent. This can be any JavaScript code, but the key object whose properties are available in the Pre-request section is request. You can access it via pm.request. When you type a dot, a dropdown list of all available methods appears.

pm.request.headers.add({
    key: "Authorization",
    value: "Bearer jwt"
});

Scripts defined in the Scripts —> Post-response (Tests) section are executed after a request has been sent and a response has been received from the server. In addition to accessing the request, you now have access to the response object. You can access it via pm.response. After typing a dot, a list of all available methods is displayed.

It is in Post-response that automated checks are most commonly written to ensure the server response meets expectations. To write a test, call pm.test and pass in any test name and a function that will be executed after the request is sent. The result of the function will set the test status to true = PASSED or false = FAILED and will be displayed in the Test Results.

pm.response.code

pm.response.json()

To sum up, scripts in Postman allow you to automate part of your work — generate test data, prepare requests, and write automated checks for server responses.

Postman’s capabilities for writing full-scale automated tests are limited, but they are sufficient for basic API testing. For comprehensive automated test scenarios, you will need to learn a programming language such as Java or Python and explore testing frameworks and tools like Selenium, Playwright, Rest Assured.