questions4

Question 1

What is strict mode in JS?

Answer 1

this is a mode that place some restrictions to your jS code for example it disables variable hoisting

Question 2

What is the error in js?

Answer 2

Errors are statements that don’t let the program run properly. There 3 types : syntax errors, runtime errors, and logical errors

Question 3

How to throw an error?

Answer 3

‘throw new Error’ syntax for errors with detailed information

Question 4

How to handle an error?

Answer 4

try - wrap weird code that may throw an error in try block.
catch - catches an error
finally - code in the finally block will always be executed no matter is there an error.

Question 5

How to work with the async error?

Answer 5

Promise has catch method it returns us the error from the failed async operation.

Question 6

let and const, compare with var

Answer 6

var can be hoisted and it can be called outside of block scope.

Question 7

Arrow functions

Answer 7

Arrow functions are always anonymous. ‘this’ refers to lexical/parent context

Question 8

Template strings

Answer 8

string that gives more control over dynamic strings.
Template literal is created using the backtick () character scfss ${fff} ffvf`

Question 9

Classes

Answer 9

Syntactical sugar. Classes are a template for creating objects. Class declarations are not hoisted.
Use class keyword to create a new class
Can be used with 'extends' keyword to make one class extended from another.
New keyword to create a new object based on class

Question 10

Symbols

Answer 10

It is a primitive type in JS. 
Symbols are often used to add unique property keys to an object.
Every Symbol() call is guaranteed to return a unique Symbol
let sym2 = Symbol('foo')