form global variable cannot update between session

Hello, I set a global variable, isFormSaved, to denote that the form is ever saved. Its default value is false.

in the form postSave event:

isFormSaved.value = "true"; // i also tried isFormSaved.value = true

in the form init event:

if(isFormSaved.value=="true")// i also tried isFormSaved.value = true

    doSomething();

When the form is first time open, isFormSaved is false. In the postSave event, it's changed to true. But when the form is reopened, init form event still shows it's false.

I use the reader extension to enable "add delete and change from fields".

Anyone has any idea? thank you.