Code not adding object to an array

Question

I'm trying to add a set of objects that have been retrieved from a JSON file into an array. I've tried using push but the result is the same. The length value of the array remains 0. What am I doing wrong? The JSON parses fine as I can get the values during the loop.

<script type="text/javascript"> 

//my array
var myArray = new Array();

function performSearch(){

    var url = "http://myjsonurl...";
    var counter = 0;

    $.getJSON(url, function(response){
         $.each(response.data.people, function() {

            //p is the the object to add to the array
            var p = new person(this.name, this.age);

            //tried using myArray.push instead of having a counter, but
            //I get the same length of 0.
            myArray[counter] = p;
            counter++;
        });

    });     

    //always returns 0  
    alert(myArray.length);

}

... 
</script>

Lycha · Accepted Answer · 2011-10-30 18:47:50Z

3

getJSON() is an asynchronous function. It only starts to fetch the data when you call it, and it calls the given function only after it has loaded it. So you call the alert before anything is fetched. You should have the alert right after the .each() function.

answered Oct 30, 2011 at 18:47

Lycha

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Comments

Matt Ball · Accepted Answer · 2011-10-30 18:51:43Z

1

Ajax is asynchronous. Whatever depends on the JSON needs to happen in the callback.

function performSearch()
{
    var url = "http://myjsonurl...";
    $.getJSON(url, function(response)
    {
        var myArray = $.map(response.data.people, function()
        {
            return new person(this.name, this.age);
        });

        alert(myArray.length);
    });     

    //always returns 0  
    alert(myArray.length);
    // that's because this code executes before the $.getJSON callback does
}

answered Oct 30, 2011 at 18:51

Matt Ball

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Comments

Guffa · Accepted Answer · 2011-10-30 18:52:00Z

1

You are returning the array before you put the objects in it.

The callback function used in the getJSON method doesn't run right away, it runs when the response arrives. As two methods can't run at the same time, you will always have exited your function before the callback function can run.

You can access the result inside the callback function:

<script type="text/javascript"> 

function performSearch(){

  var url = "http://myjsonurl...";

  $.getJSON(url, function(response){

    var myArray = [];

    $.each(response.data.people, function() {
      var p = new person(this.name, this.age);
      myArray.push(p);
    });

    alert(myArray.length);

  });     

}

</script>

answered Oct 30, 2011 at 18:52

Guffa

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Comments

Riz · Accepted Answer · 2011-10-30 18:47:43Z

0

<script type="text/javascript"> 

//my array
var myArray = new Array();
var counter = 0;

function performSearch(){

    var url = "http://myjsonurl...";

    $.getJSON(url, function(response){
         $.each(response.data.people, function() {

            //p is the the object to add to the array
            var p = new person(this.name, this.age);

            //tried using myArray.push instead of having a counter, but
            //I get the same length of 0.
            myArray[counter] = p;
            counter++;

            alert(myArray.length);

        });

    });     


}

... 
</script>

answered Oct 30, 2011 at 18:47

Riz

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1 Comment

Riz Over a year ago

assuming you need to call performSearch function multiple times.

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