[qlik sense 3.0] Question about receiving data from field programmatically

[Anonymous]

Hello, I'm new in qlik and i'm trying to work with qlik programmatically.

var field = app.field("my-field-name");
var fieldData = field.getData();

console.log("fieldData");
console.log(fieldData);
console.log(fieldData.rows.length);

As result i have array with length 0.

And of course i can't work with him.

And my question is:

What should i do to receive 12.

Thanks.