I can't access another method in javascript oop model

Question

I want to update or insert data in my database. If user is exists, update data. If not exists insert data.

That function is Database.getUser()

if (results.rows.length > 0) {
    this.updateData(results.rows[0].id, lastseen);
} else {
    this.saveData(username, lastseen);
}

this code doesn't work. I get error like this.

Uncaught TypeError: this.saveData is not a function

Uncaught TypeError: this.updateData is not a function

How can i access another method in my Database.getUser() method?

var Database = function() {
   var mydb = false;
}
Database.prototype.initDB = function() {
   try {
       if (!window.openDatabase) {
           console.log('not supported');
       } else {
           var shortName = 'tbl_xyz';
           var version = '1.0';
           var displayName = 'X Y Z';
           var maxSize = 2 * 1024 * 1024;
           this.mydb = openDatabase(shortName, version, displayName, maxSize);
       }
       console.log('Init DB');
   } catch (e) {
       console.log(e);
   }
}
Database.prototype.createTable = function() {
   try {
       this.mydb.transaction(function(transaction) {
           transaction.executeSql("CREATE TABLE IF NOT EXISTS friends (id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, username VARCHAR(50), lastseen TIMESTAMP);", [], this.nullDataHandler, this.errorHandler);
       });
       console.log('Create Table');
   } catch (e) {
       console.log(e);
   }
}
Database.prototype.errorHandler = function(transaction, error) {
   alert("Error processing SQL: " + error);
   return true;
}
Database.prototype.nullDataHandler = function(transaction, results) {}
Database.prototype.saveData = function(username, lastseen) {
   try {
       this.mydb.transaction(function(transaction) {
           transaction.executeSql("INSERT INTO friends (username, lastseen) VALUES (?,?)", [username, lastseen], this.nullDataHandler, this.errorHandler);
       });
       console.log('Save Data');
   } catch (e) {
       alert("Error processing SQL: " + e.message);
       return;
   }
}
Database.prototype.updateData = function(id, lastseen) {
   try {
       this.mydb.transaction(function(transaction) {
           transaction.executeSql("UPDATE friends SET lastseen = ? WHERE id = ?", [lastseen, id], this.nullDataHandler, this.errorHandler);
       });
       console.log('Update Data');
   } catch (e) {
       alert("Error processing SQL: " + e.message);
       return;
   }
}
Database.prototype.getUser = function(username, lastseen) {
   try {
       this.mydb.transaction(function(transaction) {
           transaction.executeSql("SELECT * FROM friends WHERE username = ?", [username], function(transaction, results) {
               if (results.rows.length > 0) {
                   this.updateData(results.rows[0].id, lastseen);
               } else {
                   this.saveData(username, lastseen);
               }
           });
       });
   } catch (e) {
       alert(e.message);
   }
}
Database.prototype.loadData = function() {
   try {
       this.mydb.transaction(function(transaction) {
           transaction.executeSql("SELECT * FROM friends ORDER BY lastseen DESC", [], function(transaction, results) {
               console.log('load OK');
               console.log(results);
               for (var i in results.rows) {
                   var row = results.rows.item(i);
                   console.log('username : ' + row.username + " | lastseen : " + row.lastseen);
               }
           });
           console.log('load Data');
       });
   } catch (e) {
       alert(e.message);
   }
}

EDIT

I change like this and it's work. Is this right?

Database.prototype.getUser = function(username, lastseen) {
    try {
        var my_this = this;
        this.mydb.transaction(
            function(transaction) {
                transaction.executeSql("SELECT * FROM friends WHERE username = ?", [username], function(transaction, results) {
                    if (results.rows.length > 0){
                        my_this.updateData(results.rows[0].id, lastseen);
                    }else{
                        my_this.saveData(username, lastseen);
                    }
                });
            });
    } catch(e) {
        alert(e.message);
    }
}

`this` is not what you think it is. See here for more info http://stackoverflow.com/questions/3127429/how-does-the-this-keyword-work — elclanrs, Mar 05 '16 at 01:43

score 0 · Accepted Answer · answered Mar 05 '16 at 02:19

You tried to use this inside the function

function(transaction, results) {
    if (results.rows.length > 0) {
        my_this.updateData(results.rows[0].id, lastseen);
    } else {
        my_this.saveData(username, lastseen);
    }
}

But the function is not a member of Database. In the function scope this is related to the object where the function is defined. I think the object is window. The approach you used in the edited version is correct.

I can't access another method in javascript oop model

1 Answers1