how can i return an array created in a loop javascript?

Question

i am trying to return a column values from database in an array,but it always returns empty array.

function Select(query, db) {
var result = new Array();
db.transaction(function(tx) {
    tx.executeSql(query, [], function(tx, rs) {
        var len = rs.rows.length;

        for (var i = 0; i < len; i++) {
            var row = rs.rows.item(i);
            result.push({latitude : row['latitude']});
        }
    });

});
return result;
}

I am sure that array is created just after for loop but returns empty at last.

Krasimir · Accepted Answer · 2013-08-26 12:23:12Z

4

You are using asynchronous functions. So, direct return will not work. You need to use callback.

function Select(query, db, callback) {
    var result = new Array();
    db.transaction(function(tx) {
        tx.executeSql(query, [], function(tx, rs) {
            var len = rs.rows.length;
            for (var i = 0; i < len; i++) {
                var row = rs.rows.item(i);
                result.push({latitude : row['latitude']});
            }
            callback(result);
        });
    });
}

Select(function(result) {
    // do something with the result
})

answered Aug 26, 2013 at 12:23

Krasimir

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3 Comments

mekafe Over a year ago

so, how can i implement callback function?should i do all asynchronous operations like database access in callback?

Krasimir Over a year ago

Yep, you can't expect that you will get the result immediately. At some point your code may work, but that's only because you didn't use the result of the async operation. Sooner or later you will meet the same problem.

mekafe Over a year ago

thanks Karsimir,it helped me a lot.I will use this frequently on my project

Richard Szalay · Accepted Answer · 2013-08-26 12:23:03Z

0

Based on your description, it sound like tx.executeSql is asynchronous. That being the case, your Select method should return a Promise (also called a Future), or otherwise push the result back to the caller.

answered Aug 26, 2013 at 12:23

Richard Szalay

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