How to save the forms data in XML format with javascript?

See the "exportXFAData" method for a full discussion of the security and Reader limitations of this method.

this.exportXFAData({
cPath: "/c/temp/myData.xml",
bXDP: false
})

With help of your answer the following solution runs successfully.

#################################################
I have created a Button with the following javascript code into the click event:
app.execMenuItem("SaveToLocalFile");

And I have create the file SaveDataToFile.js into the folder
C:\Program Files\Adobe\Acrobat 7.0\Acrobat\Javascripts :

-- Content of SaveDataToFile.js ----------------------
// create a new menu item:
app.addMenuItem({
cName: "SaveToLocalFile",
cParent: "File",
cExec: "ExpDataXml();",
cEnable: "event.rc = (event.target != null);",
nPos: 1
});


function ExpDataXml()
{
this.exportXFAData({cPath: "/c/temp/myData.xml", bXDP: false});
};
---------------------------------------------------
################################################


To understand more the security of how Acrobat allow functions tu runs i have the following question:
Why I get the following error into the Console
TypeError: this.exportXFAData is not a function
1:XFA:form1[0].#subform[0].Button3[0]:click
when I replace app.execMenuItem("SaveToLocalFile");
with this.ExpDataXml(); in the click event of the button ?
I will appreciate if you have a workaround to bypass this problem.
Thanks in advance for your help.

LiveCycle Designer designed forms are different from Acrobat designed forms, especially at the JavaScript extensions. With LiveCycle Designer you can use:

xfa.host.exportData("filename.xml", 0);

See LiveCycle Designer "Help => Scripting" for more information.,