How to tidy up my code for Unity 5 Basic Platformer

Hi guys,

I've been following a recent tutorial to set up a basic platformer. The script works, but it's a little untidy. So I thought I'd do the typical suggest to change the lengthy:

GetComponent ().velocity = new Vector2 (GetComponent ().velocity.x, jump);

to something shorter and more readable:

rb.velocity = new Vector2 (rb.velocity.x, jump );

But it just isn't working with the changes. Below is the full C# script:

 using UnityEngine;
 using System.Collections;
 
 public class PlayerController : MonoBehaviour
 {
     
     //Movement
     public float speed;
     public float jump;
     float moveVelocity;
     public Rigidbody rb;
     bool IsGrounded = true;
 
     void Start() 
     {
         rb = GetComponent<Rigidbody>();
     }
 
     void Update ()
     {
         //Jumping
         if (Input.GetKeyDown (KeyCode.UpArrow) && (IsGrounded == true))
 
         {
             //rb.velocity = new Vector2 (rb.velocity.x, jump );
             GetComponent<Rigidbody2D> ().velocity = new Vector2 (GetComponent<Rigidbody2D> ().velocity.x, jump);
         }
         
         moveVelocity = 0;
         
         //Left Right Movement
         if (Input.GetKey (KeyCode.LeftArrow)) 
         {
             moveVelocity = -speed;
         }
         if (Input.GetKey (KeyCode.RightArrow))
         {
             moveVelocity = speed;
         }
         
         GetComponent<Rigidbody2D> ().velocity = new Vector2 (moveVelocity, GetComponent<Rigidbody2D> ().velocity.y);
 
         Debug.Log(IsGrounded);
         
     }
     
     //Check if Grounded
     void OnTriggerEnter2D()
     {
         IsGrounded = true;
     }
     void OnTriggerExit2D()
     {
         IsGrounded = false;
     }
 }

Any help or suggestions how I could improve the script would be appreciated.

Thanks, Jay.