Javascript fetch JSON array

Question

I'm trying to fetch a json-array via ajax. my test.php returns:

[{"name":"James","age":24},{"name":"Peter","age":30}]

my Javascript looks like this:

var persons=new Array();
$.getJSON("../../api/test.php", function(data){
        $.each(data, function(index,value){
                    persons.push(new Person(value.name,value.age));
                });
    });

Problem is when I later call persons.length, I get Cannot read property 'length' of undefined. When I copy/paste the output of test.php from my browser into a local variable, everything works just fine:

var content=[{"name":"James","age":24},{"name":"Peter","age":30}];
for(var i=0; i<content.length; i++)
    persons.push(new Person(content[i].name,content[i].age));

What am I doing wrong?

"when I later call persons.length" - I'm guessing scope or async issue. Can you show us more context? — Jason P
– Jason P, Commented Jan 31, 2014 at 19:11
When are you trying to call persons.length? $.get is asynchronous, so it may not be done yet. — gen_Eric
– gen_Eric, Commented Jan 31, 2014 at 19:11
See "How to return the response from an AJAX call?" The difference is that $.get() is asynchronous, so data and all of the Persons created from it are available later, when the callback is called sometime after the surrounding code has continued to execute. — Jonathan Lonowski
– Jonathan Lonowski, Commented Jan 31, 2014 at 19:11
@JonathanLonowski That may be relevant, however, it doesn't explain the error that is occurring. The error states that persons is undefined, but it is clearly defined in the code he provided. — user400654
– user400654, Commented Jan 31, 2014 at 19:14
Problem solved! Thank you guys!! Thanks a lot !!! I had a method showResults() that modified my html, solution was to call it inside de $.getJSON() Async issues :D I feel so stupid right now xD — Seneca
– Seneca, Commented Jan 31, 2014 at 19:17

Jordan · Accepted Answer · 2014-01-31 19:12:52Z

6

This is probably an issue with scope. If "var persons" is declared within a function then it is in the function's scope. Double check where it is declared, and from where you are trying to access it.

For further reading see: http://coding.smashingmagazine.com/2009/08/01/what-you-need-to-know-about-javascript-scope/

Edit: I don't believe the asynchronous call $.getJSON would be the cause of the issue because persons.length would be 0 and persons would not be undefined.

var persons = new Array();
print persons.length; // ==> 0

answered Jan 31, 2014 at 19:12

Jordan

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