Show the javascript method raw  code in import 

such as a function is

function getActiveChannelID(){

let a = 10;

let b = 250;

return a+b; // noramlly it returns 260

}

now call that function in another javascript file 

let channelID = this.localStorageService.getActiveChannelID; // without first bracket it  returns the raw code

alert(channelID) //returns the raw code of getActiveChannelID method

now if you want to get the value what the  getActiveChannelID method returns use first braket() after the method.