Question

I would like to declare a global variable that takes value from DataStore and display its value in the alert Window.

var params = 1;

var storeTeacher = new Ext.data.JsonStore({
       id: 'IDstoreTeacher',
       url: 'school.php',
       method: 'POST',
       baseParams:{task: "LABEL",
                   parametar: params},
       root: 'rows',
       fields: 
              [{name: 'NameT', type: 'string', mapping: 'Teacher_name'}],
       autoLoad: true   
    });

var TeacherName;

storeTeacher.load({ 
       scope: this, 
       callback: function (records, operation, success) { 
                   TeacherName = storeTeacher.getAt(0).get('NameT');
              }
});


alert(TeacherName);

But, only thing I get is the alert Window that says: undefined

Answer 1

Your alert(TeacherName); call is being executed before the callback on your storeTeacher.load callback is being executed.

If you put the alert(TeacherName) in the callback function it will populate your TeacherName properly and show correctly in the alert:

storeTeacher.load({
    scope: this,         
    callback: function (records, operation, success) {                     
        TeacherName = storeTeacher.getAt(0).get('NameT');
        alert(TeacherName);   
} }); 

This behavior is expected.