Placing HTTP address in javascript variable for json parsing

If I am to have this external json file:

{
"http://example.org/about" :
    {
        "http://purl.org/dc/elements/1.1/title" : [{"value" : "annas homepage" , "type" : "literal"}]
    }
}

and this external jquery script that fetches title of the book inside json file:

var a = 'http://example.org/about'
var b = 'http://purl.org/dc/elements/1.1/title'

$(document).ready(function() {
  $("#trigger").click(function(event) {
    $.getJSON('rdfjson.json', function(json) {
      $('#meta').html('Title: ' + json.a.b[0].value);
    });
  });
});

and this HTML code:

<p>Click on the button to fetch data from json structure:</p>
<div id="meta">
This text will be overwritten.
</div>
<input type="button" id="trigger" value="Load Data" />

Why wouldn't it work? When I use normal strings inside json document and script, it works OK.

Also, I don't understand how could I iterate through the whole json file if it is, for example, more complex or elements have long vectors containing data etc etc..

Thanks a lo开发者_Python百科t!

Because you're looking for an object member named a, rather than an object member whose name is the value stored in the variable "a".

Instead of using "dot notation", use "square bracket notation"

$('#meta').html('Title: ' + json[a][b][0].value);

For more information, see here: http://www.dev-archive.net/articles/js-dot-notation/

Edit:

If the JSON structure varies like so:

1. Version One:

   {
       "http://example.org/about" :
       {
           "http://purl.org/dc/elements/1.1/title" : [{"value" : "annas homepage" , "type" : "literal"}]
       }
   }
   

2. Version Two:

   {
       "http://somewhereelse.com/something" :
       {
           "http://anotherplace.org/dc/blah-blah-blah/title" : [{"value" : "annas homepage" , "type" : "literal"}]
       }
   }
   

e.g. there is always one object, which has one member which has one member

... and you need to target it:

$.getJSON('rdfjson.json', function(obj) {
  for (var x in obj) {
      if (obj.hasOwnProperty(x)) {
         var obj2 = obj[x];

         for (var x in obj2) {
            if (obj2.hasOwnProperty(x)) {
                $('#meta').html('Title: ' + obj2[x][0].value);
            }
         }
      }
  }
});

You can of course add conditionals within the for loops if you know a little bit more information about the path you need to traverse:

$.getJSON('rdfjson.json', function(obj) {
  for (var x in obj) {
      // if you know you're looking for a key that begins with "http://"
      if (obj.hasOwnProperty(x) && x.indexOf("http://") === 0) { 
         var obj2 = obj[x];

         for (var x in obj2) {
            // Check that the value is an array of at least length 1, and whose 1st value has the property "value".
            if (obj2.hasOwnProperty(x) && obj2[x] instanceof Array && obj2[x].length > 0 && obj2[x][0].value) { 
                $('#meta').html('Title: ' + obj2[x][0].value);
            }
         }
      }
  }
});

  $('#meta').html('Title: ' + json.a.b[0].value);

should be

  $('#meta').html('Title: ' + json[a][b][0].value);

Use the square brackets like sp:

json[a][b][0].value

Small test case here: http://jsfiddle.net/sSbtq/

You need to use square bracket notation:

json[a][b][0].value

which will allow you to select properties using variables (which you cannot do with dot notation).

See http://www.jibbering.com/faq/faq_notes/square_brackets.html