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1. var & let

- var gets hoisted. can be used before declaration. let not hoisted

- var function scope & let block scope

2. == & ===

- == compares content only

- === compares both content as well as type

- (e.g. '1' == 1 => true .... '1' === 1 => false )

3. let vs const

- let - can be reassigned

- const -- can't be reassigned. **The content of array however can be modified *(const array.push is possible in const)

- const should not be declared undefined . we can't re-assign it. compile error.

4. undefined vs null

- typeof(undefined) => undefined ------ typeof(null) => object

- declared variable but not define - undefined is assigned by default

hoisting in JS

$$$$$$$$$$fat arrow functions :- https://medium.com/@thejasonfile/es5-functions-vs-es6-fat-arrow-functions-864033baa1a

prototypal inheritance :-

async javascript promises etc,

closures in depth

prototype & prototype chaining