postman body get the last 3 characters on the username

Question

{
    "data": {
        "username": "tell1535",
        "password": "{{encryptedPassword}}",
        "type": "session"
    }
}

this is the body of my postman request is there a way to use the value of username in pre request tab and set a value like

pm.environment.set("number", usernamelast4digits)

Update:

Answer 1

This is overview

How to use Postman's global variable for username and number by JSON.parse(pm.request.body.toString())

By JavaScript commands (slice) in Pre-request Script tab from input body.

Demo by Flask and Postman To save as server.py

It has one post API.

The post API forward from the input POST body to the output body.

from flask import Flask, jsonify, request
import jwt

app = Flask(__name__)
    
@app.route("/sessions", methods=["POST"])
def post_test():
    content_type = request.headers.get('Content-Type')
    if (content_type == 'application/json'):
        json = request.get_json()
        encoded_jwt = jwt.encode({'username': json['data']['username']}, 'secret', algorithm='HS256')
        newJson = {
            'data' : {
                'type': 'session',
                'token': encoded_jwt
            }
        }
        return jsonify(newJson), 201
    else:
        return 'Content-Type not supported!'

if __name__ == "__main__":
    app.run(debug=True)

Install Dependency

pip install flask
pip install pyjwt

Run server

python server.py

Example POST call

http://127.0.0.1:5000/sessions

Input Body

{
    "data": {
        "username": "tell1535",
        "password": "{{encryptedPassword}}",
        "type": "session"
    }
}

Pre-request Script

var jsonData = JSON.parse(pm.request.body.toString());
console.log(jsonData);
pm.globals.set("username", jsonData.data.username);
pm.globals.set("number", jsonData.data.username.slice(-4));
console.log(pm.globals.get("username"));
console.log(pm.globals.get("number"));

Output Body

{
    "data": {
        "token": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VybmFtZSI6InRlbGwxNTM1In0.V8tbNNjiEtv3MBYmwX82W-t0y0bnfLER48a9pQiK8m0",
        "type": "session"
    }
}

Send POST API

After send POST API encryptedPassword need to assign by manually.

username and number will assign.

And debug the variable log from Postman console.

Conclusion

API's output will create token by Flask JWT logic. The number variable picked up from input body by last 4 digit of username.