Using a JSON file to store a small database persistently, in javascript

Question

I am new to the use of JSON.

I want my webpage to display, in a table, a small database of a few hundred records. Wanting to avoid the hassle of putting my data in a MySQL database or something similar, I figured I would read my data from a JSON file, and write it out to a JSON file, and that this would amount to convenient, persistent storage of my database at my website.

So I spent a bit of time writing a script that translated my existing papers file into a papers.json file that contains all my records. It looks like:

[
  {"title" :  "IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture",
   "authors" :  "IEEE",
   "pub" :  "IEEE 802-2001 standard",
   "datepub" :  "2001",
   "keywords" :  "MAC",
   "dateread" :  "200309",
   "physloc" :  "box i",
   "comment" :  "Indicates how you can manage addresses assigned to you by IEEE."
  },
  {"title" :  "A framework for delivering multicast messages in networks with mobile hosts",
   "authors" :  "A. Acharya, B. R. Badrinath",
   "pub" :  "Mobile Networks and Applications v1 pp 199-219",
   "datepub" :  "1996",
   "keywords" :  "multicast mobile MH MSS",
   "dateread" :  "",
   "physloc" :  "box a",
   "comment" :  ""
  },

    <hundreds more similar papers records here...>

  },
  {"title" :  "PiOS: detecting privacy leaks in iOS applications",
   "authors" :  "M. Egele, C. Kruegel, E. Kirda, G. Vigna",
   "pub" :  "NDSS 2011",
   "datepub" :  "2011",
   "keywords" :  "iOS app location leakage",
   "dateread" :  "",
   "physloc" :  "box e",
   "comment" :  "discussed at Latte"
  }
]

Here is the javascript code I am using to read it. (I haven't yet coded the write-out of the records, because the read isn't working.)

var pdb = []; // global

var doneReading = false; //global

$(document).ready(function() {
        $.getJSON('papers.json',function(data) {
            pdb = data;
            doneReading = true;
        });

        while (!doneReading) {}

        alert("finished assignment of JSON to pdb"+" "+typeof pdb); 
        //alert(pdb[0].title);
        console.log(pdb[2]);
        //setup();
});

The script hangs in the while loop forever. Why?

Also I am new to jQuery. I would feel more comfortable doing this without the use of a library, one new thing at a time being enough for me. Can one manipulate JSON files easily without jQuery?

Uhhh why not just put the alert / log in the getJSON callback? — asawyer
– asawyer, Commented May 25, 2012 at 18:32
OK Thanks. By changing my code to this, it worked: $(document).ready(function() { $.getJSON('papersdb.52.json', pdb, function(data) { pdb = data; alert(pdb[1].title); }); }); — user1416227
– user1416227, Commented May 25, 2012 at 18:43
I used to make ajax calls to RESTful web api services, I've never tried to do a local storage thing so.... I dunno. I do know that if you take a look at Backbone.Js they have a local storage plugin that makes model persistence to local seamless. — asawyer
– asawyer, Commented May 25, 2012 at 18:48

apsillers · Accepted Answer · 2012-05-25 18:32:36Z

3

Normal browser JavaScript is single-threaded. Precisely because the infinite while never ends, the JavaScript engine never gets to process the success callback of the $.getJSON call. Your browser's sole JS thread sits looping forever and never moves on to the callback.

Solution: You should eliminate the loop and move code that is currently after the infinite loop into your $.getJSON callback.

answered May 25, 2012 at 18:32

apsillers

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2 Comments

user1416227 Over a year ago

Is there a simple way to use JSON without jQuery.getJSON?

apsillers Over a year ago

You can just use Ajax for same-domain requests, but it will mean longer code and has no real benefit over $.getJSON (other than learning basic JS, which is a fine goal).

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