Html5 declares that the statuses of values are not defined

Question

Html5 declares that the statuses of values are not defined

In a chrome extension, I am encountering an issue with the following code:

var DB = openDatabase('CMPDB', '1.0', 'Database for CMP', 4 * 1024 * 1024); 
LoadFromDB();   

function LoadFromDB() {

    DB.transaction( function(tx)
    {           
        tx.executeSql('CREATE TABLE IF NOT EXISTS table(X, Y, Z UNIQUE)');

        tx.executeSql('SELECT * FROM table', [], function (tx, results) {
            var len = results.rows.length;
            for (i = 0; i < len; i++) {                 
                alert(results.rows.item(i).X.text);
                alert(results.rows.item(i).Y.text);
                alert(results.rows.item(i).Z.text);                         

            }
        });
    });
}

I'm puzzled as to why all of the alerts are returning undefined even though the table has been created beforehand and the Chrome Dev tools show that values exist in the table. Any insights on this perplexing situation?

javascript sql database sqlite client-side

Answer 1

Answer №1

It seems that your SELECT statement may be running before the table is fully created. You could consider placing your SELECT query inside a callback function to ensure it is executed after the CREATE TABLE SQL command has finished. Here's an example:

tx.executeSql('CREATE TABLE IF NOT EXISTS table(A, B, C)', function(tx) {
    tx.executeSql('SELECT * FROM table', [], function (tx, results) {
        var length = results.rows.length;
        for (index = 0; index < length; index++) {                 
            console.log(results.rows.item(index).A.text);
            console.log(results.rows.item(index).B.text);
            console.log(results.rows.item(index).C.text);                         
        }
    });            
});

Answer 2

It seems that your SELECT statement may be running before the table is fully created. You could consider placing your SELECT query inside a callback function to ensure it is executed after the CREATE TABLE SQL command has finished. Here's an example:

tx.executeSql('CREATE TABLE IF NOT EXISTS table(A, B, C)', function(tx) {
    tx.executeSql('SELECT * FROM table', [], function (tx, results) {
        var length = results.rows.length;
        for (index = 0; index < length; index++) {                 
            console.log(results.rows.item(index).A.text);
            console.log(results.rows.item(index).B.text);
            console.log(results.rows.item(index).C.text);                         
        }
    });            
});

Html5 declares that the statuses of values are not defined

Answer №1

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