Q: How to differentiate variable in strict mode than the normal mode? ===================================================================== In general: variable need not declared in JS when the strict mode is disabled. ==> In strict mode, the variable can be three conditions: 1) Declaration ==> let/var/const 2) Assignment 3) Initialization Document ================================================== JavaScript Comments: ==================== ==> Comments can be used for readability. ==> Two ways: 1) Single Line Comments ==> // 2) Multi Line Comments ==> /* comments are here */ ==> in anywhere of the program. Document ======================================================= JavaScript Datatypes: ===================== Datatype ==> type of the data to store in the variable. ex: application form: ================= User name ==> string age ==> integer salary ==> double/float etc. ==> Datatypes are classified into two types: 1) Primitive Datatypes All fundamental datatypes are always define with single literal ex: x = 10, salary = 55000.0; etc. 2) Non-Primitive Datatypes All Collection types are always define with more than one literal Ex: "JavaScript", [1,2,3,4,5,6], {'a':10,'b':20} Primitive Datatypes =================== Number Boolean Number ====== Document ========================================================= Boolean ======= true, false Document =================================================== Non-Primitive Datatypes ======================== Strings Objects ==> Arrays, Maps Document ============================================= Document