Storing ajax output into variable

Question

I have to check weather invoice number is duplicate or not for that i am using following ajax.

function check_duplicate_invoice(num){
          var isDuplicate ;

          xmlhttp = new XMLHttpRequest();
           xmlhttp.open("GET","check_duplicate_invoice.php?in="+num, true);
           xmlhttp.send();
           xmlhttp.onreadystatechange = function() {
                if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {

                    isDuplicate =xmlhttp.responseText.trim() // reponceText will be 0 or 1
                }
            }

            alert(isDuplicate); //result undefined

            if(isDuplicate== 1){
                alert("Invoice Number Already Exist");
            }
    }

I am not able to store ajax output into isDuplicate variable. Please help.

Did you try to alert xmlhttp.responseText.trim() in the first place to see if it has a value at all? — icecub
– icecub, Commented Sep 19, 2015 at 1:22
you should use alert(isDuplicate) inside the success function. in your case. the xmlhttp.readyState == 4... — roullie
– roullie, Commented Sep 19, 2015 at 1:23
@roullie Could be me, but since he's declaring the variable outside the function, but within the same function as the alert, that shouldn't matter. — icecub
– icecub, Commented Sep 19, 2015 at 1:26
If you are using jQuery you can make you life easier, if you use $.ajax or $.get methods — gre_gor
– gre_gor, Commented Sep 19, 2015 at 1:29
@icecub It does matter, since he is calling that alert before that AJAX request returns the data. That's why isDuplicate is undefined. — gre_gor
– gre_gor, Commented Sep 19, 2015 at 1:34

e4c5 · Accepted Answer · 2015-09-19 01:24:09Z

1

That's because ajax calls are asynchronous. You are looking at the variable before the request has had a time to complete. Try this:

function check_duplicate_invoice(num){
      var isDuplicate ;

      xmlhttp = new XMLHttpRequest();
       xmlhttp.open("GET","check_duplicate_invoice.php?in="+num, true);
       xmlhttp.send();
       xmlhttp.onreadystatechange = function() {
            if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {

                isDuplicate =xmlhttp.responseText.trim() // reponceText will be 0 or 1
                alert(isDuplicate); //result undefined

                if(isDuplicate== 1){
                   alert("Invoice Number Already Exist");
                }

            }
        }

}

answered Sep 19, 2015 at 1:24

e4c5

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6 Comments

priyesh kanodiya Over a year ago

Tried your answer its working in firefox but not in chrome browser. I have to use this in crome. Please help in this matter

e4c5 Over a year ago

what happens in Chrome?

priyesh kanodiya Over a year ago

Nothing happens in Chrome

e4c5 Over a year ago

Something would definitely be happening in chrome. Open the developer console and check for errors. Post the code that calls this method (update your question with that code)

priyesh kanodiya Over a year ago

I dont know how to use developer console for finding errors. Can you please help

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