ReactJS - Alert is looping many times after function is called inside an if() statement

Calling **`this.mobile(this.state.number)`** function will cause a loop of 10-12 iterations of the `alert()`

Can you explain me please why ?

 checkNum = () => {
    const submit = document.getElementById('mySubmit');
    submit.addEventListener('keyup', (event) => {
      if (event.key === 'Enter' && this.mobile(this.state.number))  
        //calling from here 
      {
        this.setState({ mobileNum: this.state.number });
      }
    });
  };

      mobile = (e) => {
        let num = /^0(5[^7]|[2-4]|[8-9]|7[0-9])[0-9]{7}$/;
        const isRight = num.test(e);  
        alert(`The number you've entered is ${isRight}`);
        return isRight;
      };

Thanks