Continuous Shooting

 [SerializeField] GameObject laserFire;
 [SerializeField] float projectileSpeed = 20f;
 private float projectileFiringPeriod = 0.1f;

 Coroutine firingCoroutine;

 void Update()
 {
     Fire();
 }

 IEnumerator FireContinuously() {

     while (true)
     {
         GameObject laser = Instantiate(laserFire, transform.position, Quaternion.identity) as GameObject;
         laser.GetComponent<Rigidbody2D>().velocity = new Vector2(0, projectileSpeed);
         yield return new WaitForSeconds(projectileFiringPeriod);
     }
 }

 private void Fire() {

     if (Input.GetButtonDown("Fire1"))
     {
       firingCoroutine =  StartCoroutine(FireContinuously());
     }
     if (Input.GetButtonUp("Fire1"))
     {
         StopCoroutine(firingCoroutine);
     }
 }