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Scripts in Requestly allow you to extend and customize your API requests and responses dynamically using JavaScript. These scripts enable you to manipulate requests before they are sent (Pre-request scripts) or process responses after they are received (Post-response scripts). With access to the full request and response objects, you can achieve advanced automation, validations, and transformations.

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Pre-Request Scripts

Pre-Request Scripts run before the API request is sent to the server. They allow you to modify request attributes, such as headers, body, query parameters, or even the URL. Pre Scripts are useful for adding authentication tokens, generating timestamps, or altering the request dynamically based on certain conditions. Let’s try to understand the workings of pre-script using easy-to-follow examples. Auto Increment Page Numbers Let’s assume you have an endpoint that takes page number as query parameter, we use environment variable {{page_number}} to get value of page number. 
https://app.requestly.io/echo?page={{page_number}}
We can get current page number from environment variables and set it back with an increment. 
rq.environment.set("page_number", rq.environment.get("page_number")+1);
Now every time you click the Send button of this request it would send incremented page number. Test APIs by Randomising Values During development hitting an API with new data every time can be a pain, we can use Pre-Script to randomise the values and call the same API without getting duplicate entry error. Let’s setup our request with body as follows: 
POST: <https://app.requestly.io/echo>

{
	"name": "{{name}}",
	"email": "{{email}}",
	"phone_number": "{{phone_number}}"
}
We will use below pre-script to create random values and update them in environment variables. 
var name = (+new Date).toString(36).slice(-5);
var phone = Math.round((Math.random())*(10**10));
rq.environment.set("name", name);
rq.environment.set("email", name+"@example.com");
rq.environment.set("phone_number", phone);
You can also use pre-script to generate access tokens, validate the requests, generate some random data for the request. You can also access elements of the request, collection variables and environment variables, checkout Requestly’s JavaScript API.

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Post-Response Scripts

Post-Response Scripts run after the API response is received. They allow you to process response data, validate outputs, or log details for debugging. Post Scripts are useful for transforming the response body, validating response codes, or storing results for further use. Let’s try to understand the working of post script using easy to follow examples. Validate Response Code 
if (rq.response.code !== 200) {
    console.error("Unexpected Response Code:", rq.response.code);
}
We can also fetch and set API Keys or auth tokens, id, and other data from response of an API and use it in other APIs. You can access elements of the request, response, collection variables and environment variables, checkout Requestly’s JavaScript API.

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Requestly JavaScript API rq

Requestly provides a robust set of JavaScript properties and methods to interact with API requests, responses, environments, and global variables. Below is a detailed documentation of these features, explaining each property and function with examples.

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Request Object rq.request

These properties and methods let you access the details of the API request in scripts. rq.request.method Use this property to get the Request’s method. The HTTP method of the request (e.g. GET, POST, PUT, OPTION, DELETE, PATCH, HEAD). Example: 
console.log("Request Method: ", rq.request.method);
rq.request.headers An list of header rows each having key, value & isEnabled for each custom header you create. Example: 
console.log("Headers: ", JSON.stringify(rq.request.headers));
rq.request.body The body of the request, accessible as a string. If you have selected Form under Body it would be returned in object format. Example: 
console.log("Body:", JSON.stringify(rq.request.body));
rq.request.url The full URL of the API request. Example: 
console.log("Request URL:", rq.request.url);
rq.request.queryParams An object containing rows of query parameters each having key, value & isEnabled. Example: 
console.log("Query Params:", JSON.stringify(rq.request.queryParams));

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Response Object rq.response

These properties and methods let you access the details of the API’s response in scripts. rq.response.body The body of the response as a string. Example: 
console.log("Response Body:", rq.response.body);
rq.response.responseTime The time taken by the request to complete, in milliseconds. Example: 
console.log("Response Time:", rq.response.responseTime);
rq.response.headers An list of header rows each having key, value for each custom header you create. Example: 
console.log("Response Headers:", JSON.stringify(rq.response.headers));
rq.response.code The HTTP status code of the response. Example: 
console.log("Response Code:", rq.response.code);

if (rq.response.code !== 200) {
    console.error("Unexpected Response Code:", rq.response.code);
}
rq.response.json() Parses the response body as JSON and returns it as a JavaScript object. Example: 
console.log("Response JSON:", JSON.stringify(rq.response.json()));
rq.response.text() Returns the response body as a plain string. Example: 
console.log("Response Body as String:", rq.response.text());

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Environment Variables Object rq.environment

Environment methods let you dynamically manage environment variables during script execution. rq.environment.set(key, value) Sets an environment variable with the given key and value. Example: 
rq.environment.set("authToken", "Bearer <TOKEN>");
rq.environment.get(key) Retrieves the value of the specified environment variable. Example: 
const token = rq.environment.get("authToken");
console.log("Token:", token);
rq.environment.unset(key) Removes the specified environment variable. Example: 
rq.environment.unset("authToken");

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Collection Variables Object rq.collectionVariables

Collection variables are scoped to a specific collection. Unlike environment variables (scoped to a specific environment), collection variables are only accessible within the requests that belong to a given collection.

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rq.collectionVariables.set(key, value)

Creates or updates a collection variable with the given key and value. Example: 
rq.collectionVariables.set("basePath", "/v1/users");

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rq.collectionVariables.get(key)

Retrieves the value of the specified collection variable. Example: 
const path = rq.collectionVariables.get("basePath");
console.log("Collection Variable basePath:", path);

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rq.collectionVariables.unset(key)

Removes the specified collection variable. Example: 
rq.collectionVariables.unset("basePath");

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Global Variables Object rq.globals

Global variables work similarly to environment variables. Global variables are available to all collections and requests. rq.globals.set(key, value) Sets a global variable with the given key and value. Example: 
rq.globals.set("appVersion", "1.0.0");
rq.globals.get(key) Retrieves the value of the specified global variable. Example: 
const version = rq.globals.get("appVersion");
console.log("App Version:", version);
rq.globals.unset(key) Removes the specified global variable. Example: 
rq.globals.unset("appVersion");