getAll() , getFilteredAndSorted() & getElements() returning empty array

This below is my code.
update12() method is called on click of a button in the same page.

update12() {
let data1 = [], data2 = [], data3 = [];
this.source.getFilteredAndSorted().then(value => {
value.forEach(element => {
data1.push(element);
})
})
this.source.getElements().then(value => {
value.forEach(element => {
data2.push(element);
})
})
this.source.getAll().then(value => {
value.forEach(element => {
data3.push(element);
})
})
}

In all the above 3 cases, the value is coming as an empty array

Outside constructor in the class i have
source: LocalDataSource = new LocalDataSource();