javascript - why java script doesn't stack inside the while loop

itemprop="text">

I am trying to check values
from a database through sending the values by for loop in ajax request to php file,
"each value in request" then the file return variable called "avl" if
$data["avl"]==1 so it is available if not it is not available.

The problem is that I check a stream of values
and they all must return 1 to continue my process, but the
condition doesn't wait until the for loop ends to check. It checks the condition before
the for loop starts, even the code is not like that. Ex: it does the condition in line
100 before for loop ends in line
50.

var cartItemContainer =
            document.getElementsByClassName('cart-items')[0]
var cartRows =
            cartItemContainer.getElementsByClassName('cart-row')
var avl_qty =
            1;
for (var i = 0; i < cartRows.length; i++) {
 var
            cartItemContainer =
            document.getElementsByClassName('cart-items')[0]

 var cartRows =
            cartItemContainer.getElementsByClassName('cart-row')
 var cartRow =
            cartRows[i]

 var titleElement =
            cartRow.getElementsByClassName('cart-item-title')[0]
 var item =
            titleElement.innerText
 var quantityElement =
            cartRow.getElementsByClassName('cart-quantity-input')[0]
 var
            freequantityElement =
            cartRow.getElementsByClassName('cart-quantity-free-input')[0]

 var
            quantity = quantityElement.value
 var freequantity =
            freequantityElement.value


 alert("before avilability
            ajax")

 $.ajax({
 url: "checkavlqty.php",

            method: "POST",
 data: {

 item: item,

            quantity: quantity,

 freequantity: freequantity

            },
 dataType: "JSON",
 success: function(data) {

            alert(JSON.stringify(data));
 if (data["avl"] == 0) {
 alert("inside
            condistion")
 avl_qty = 0;
 }
 }


            })

}

alert(avl_qty)

It
always alerts 1, even the final value of avl_qty is
0.

itemprop="text">

class="normal">Answer

The ajax
call you are doing inside the loop is asynchronous, this means that when the execution
reaches the $.ajax[...] line, it will run "in the background"
while the normal execution continues through the loop.

What is most likely happening in
your code is that the execution will reach the alert(avl_qty)
line before the ajax responses from the loop reach you. You can test this by letting the
script run. You'll see that it will execute the alert("before avilability
ajax"), then alert(avl_qty) and finally all the
alert(JSON.stringify(data)); from the ajax
requests.

To solve the issue you will have to
wait for the async calls to finish, href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function"
rel="nofollow noreferrer">you can use async/await or even callbacks, href="https://stackoverflow.com/questions/14031421/how-to-make-code-wait-while-calling-asynchronous-calls-like-ajax">here's
an example.