How to set command line field in js field as required field?

Question

How to set a text field field in an invitation field as a required field?

var answer=prompt('Reason for deletion?');

Answer 1

Since it window.promptis modal, you can use the following logic:

while(!answer){
    var answer=prompt('Reason for deletion?');
};

-jsFiddle -

Answer 2

    var answer=prompt('Reason for deletion?');
    if(answer !=null)
    {
    /* Your code */
    }
    else if(!answer)
    {
    alert('Entry Required');
    return false;
    }
else
{
alert('Entry Cancelled By User');
    return false;
}

Use this and also check this