Optional Chaining

SLIDE 1
Optional Chaining ?.

SLIDE 2
When you try to access a property of undefined or null you'll get an error
```js
const user1 = {
	username: 'avikki_coder',
	address: {
		city: 'Banglore',
		pinCode: '560007' 	
	},
	print(){ console.log(this.username+'😎') }
}

const user2 = {
	username: 'cool_guy'
}

console.log(user1.address.city) // Banglore
user1.print() // avikki_coder😎

console.log(user2.address.city) 
// ❌ Cannot read property 'city' of undefined
user2.print()
// ❌ user2.print is not a function
```

SLIDE 3
Best solutions in current JS version is to use &&
```js
console.log( user2.address && user2.address.city )
// undefined

// same for function call
user2.print && user2.print()
```
Expression evaluation works from left to right
Value of a && operation is falsy if any of the value is falsy 
errors.username is undefined so expression after it is skipped.

🎉🎉 we didn't trigger any errors
but it is not a very good looking syntax

SLIDE 4
Optional Chaining to rescue😎
```js
console.log(user2?.address?.city) // undefined

user2.print?.()
```
If expression before ?. is undefined or null, anything after that is ignored and end result is undefined.

SLIDE 5

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