how to get value from js alert message to store in PHP varible?


I am trying to learn php and js. Here I am trying to put a value in php varible from javascript alert message input box but failed.
here what I have done so far,

// <?PHP and other variable is here....

			function number{
				if (fail == "") {
					number = prompt('Please enter Phone Number')
					if (number == "" || number == null) { 
						alert(' You have not specified the Phone Number. Please try again.'); 
						return false;
					else {
						return true;
				else { alert(fail); return false; }

So, actually how I can store the value from js alert to php varible? help me. Thanks for your valuable time and opinion.


PHP runs on the server side, once it’s done it sends the completed document to the users browser.

Then JS runs in the users browser.

JS can not simply store/update variables in PHP as the PHP is no longer running. You also have no such connection between the client side and the server side.

If this is for a form then simply update the form value with JS, when you submit the form PHP should get all the form data.

If this is only to enter a phone number then you might consider looking into doing an AJAX request from JS to PHP after the user inserts a phone number. You will then have to create a PHP file that handles this request spesifically and stores the phone number.