Question

First I know WebKit do not allow Make synchronous requests to SQLite database. And I’m start playing with it and tried to assign result to global variable “data”. I still not sure if it’s possible but want to ask you.

1. I’m created global object to store respond from DB

   var data = {};

2. Here is DB class

var db = {
        mydb: false,
        init: function () {
            try { 
                if (!window.openDatabase) { 
                    alert('not supported'); 
                } else { 
                    this.mydb = openDatabase('test_db', '1.0', 'Test DB', 1024*1024*5); 
                }
            } catch(e) { 
                // Error handling code goes here. 
                if (e == INVALID_STATE_ERR) { 
                    // Version number mismatch. 
                    alert('Invalid database version.'); 
                } else { 
                    alert('Unknown error '+e+'.'); 
                } 
                return; 
            }
        },
        exec: function (query, params) {
            try {
                this.mydb.transaction(function(transaction) {
                    transaction.executeSql(query, params, db.dataHandler, db.errorHandler);
                });
            } catch(e) {
                alert(e.message);
            }
        },
        dataHandler: function (transaction, results) {
            // Handle the results
            data = results.rows;
            return true;    
        },
        errorHandler: function (transaction, error) {
            // returns true to rollback the transaction
            alert('Code: '+error.code+'\nMessage: '+error.message);
            return true;
        },
    }

1. And finally here is the problem:

$(function () {
    db.init();
    db.exec('SELECT * FROM errors;');
    alert(Log.object_toString(data) ); // this alert show empty object as I declared in first line 
    alert(Log.object_toString(data) ); // this one return object with responded data from database
});

So the problem is I can’t manipulate with “data” right after db.exec() call, but if I make alert() after transaction then data will populate with all information.

Any ideas how can I avoid it?

Answer 1

I would assume that you’re making an asynchronous AJAX call, so your alert() fires before the response is received.

EDIT: As @Nick noted, this is not AJAX, but is an issue with it being asynchronous.

I don’t know anything about the API you’re using, but it would seem as though your alerts should be inside the dataHandler method:

dataHandler: function (transaction, results) {
    // Handle the results
    data = results.rows;
    alert(Log.object_toString(data) ); 
    alert(Log.object_toString(data) );
    return true;    
},

Or should be in some other function that is called from inside dataHandler.

dataHandler: function (transaction, results) {
    // Handle the results
    data = results.rows;
    someFunction( data );
    return true;    
},

// ...

function someFunction( data ) {
    alert(Log.object_toString(data) ); 
    alert(Log.object_toString(data) );
}

The reason an alert() in between makes it work, is that the pause gives the response a chance to return before the other alerts run.