ES6

Question 1

What is a code block? What are some examples of a code block?

Answer 1

A block of code that contains statements that you want to execute together contained within curly braces {}
Function, conditional, loop code block

Question 2

What does block scope mean?

Answer 2

Can’t access variables within the block, outside of the block

Question 3

What is the scope of a variable declared withconstorlet?

Answer 3

Block-scoped

Question 4

What is the difference betweenletandconst?

Answer 4

Let: mutable, not initialized to any value, and not attached to the global object as a property

Const: read-only reference, can’t be reassigned (immutable), need to initialize the value to the variable declared, constant identifiers are in uppercase

Question 5

Why is it possible to.push()a new value into aconstvariable that points to anArray?

Answer 5

An array is a special type of object and the property of aconstobject can be change but it cannot be change to reference to thenewobject

Not changing the variable name binding, mutating the content of the array which are mutable

Question 6

How should you decide on which type of declaration to use?

Answer 6

Use const until you need to reassign the value of the variable, then use let

Question 7

What is the syntax for writing a template literal?

Answer 7

String must be wrapped with backticks ( string )
Embedded JavaScript expressions wrapped with ‘$’ and ‘{}’, ${expression}
If string contains a backpack, it must be escaped using a backslash ( \ )

Allows for multi-line strings, string interpolations with embedded expressions, and tagged templates

Question 8

What is “string interpolation”?

Answer 8

Insert, or interpolate, variables into strings using template literals. Use placeholders of the form ${expression} to perform substitutions for embedded expressions

Question 9

What is destructuring, conceptually?

Answer 9

Unpack values from arrays, or properties from objects, into distinct variables

Question 10

What is the syntax forObjectdestructuring?

Answer 10

const { var1, var2: varAlias2 } = obj

Use (:) colon to rename variable

Question 11

What is the syntax forArraydestructuring?

Answer 11

const [var1, var2, var3] = arr

Use (,) to skip elements in array

Question 12

How can you tell the difference between destructuring and creatingObject/Arrayliterals?

Answer 12

When destructing, the curly or square brackets appear on the left of the assignment operator, however when creating object or array literals the brackets appear on the right

Question 13

What is the syntax for defining an arrow function?

Answer 13

(param1, param2) => {
return;
};

param => exp; // implicit return

() => exp;

Question 14

When an arrow function’s body is left without curly braces, what changes in its functionality?

Answer 14

Function body evaluated as an expression and implicit return

Question 15

How is the value ofthisdetermined within an arrow function?

Answer 15

Arrow functions don’t have their own bindings to this; have lexical scoping to this context. Takes this from the enclosing function, value of this it determined when the function is defined.

(Versus ES5 function definition, value of this is determined when the function is called.)

Question 16

What are the three states a Promise can be in?

Answer 16

Pending: initial state, neither fulfilled nor rejected
Fulfilled: meaning that the operation was completed successfully
Rejected: meaning that the operation failed

Question 17

How do you handle the fulfillment of a Promise?

Answer 17

.then((value) => { /* fulfillment handler */ })

Question 18

How do you handle the rejection of a Promise?

Answer 18

.then((reason) => { /* rejection handler */ })

Question 19

What isArray.prototype.filteruseful for?

Answer 19

Creates a shallow copy of a portion of a give array, filtered down to just the elements from the given array that past the test implemented by the provided function

Question 20

What isArray.prototype.mapuseful for?

Answer 20

Creates a new array populated with the results of calling a provided function on every element in the calling array

Question 21

What isArray.prototype.reduceuseful for?

Answer 21

Takes all of the elements in an array and reduces them into a single value

Question 22

What is “syntactic sugar”?

Answer 22

Syntax within the programming languages that is designed to make things easier to read or to express. Makes the language “sweeter” for human use: things can be expressed more clearly, more concisely, or in an alternative style that some may prefer.

Question 23

What is thetypeofan ES6 class?

Answer 23

function

Question 24

Describe ES6 class syntax.

Answer 24

class className {
  constructor(parameter) {
    // constructor code block;
  }
  method() {
    // method code block;
  }
}

Question 25

What is “refactoring”?

Answer 25

The process of restructuring existing computer code - changing the factoring - without changing its external behavior. It intended to improve the design, structure, and/or implementation of the software (its non-functional attributes), while preserving its functionality.

Question 26

How are ES Modules different from CommonJS modules?

Answer 26

ES Modules is the standardized module system for JavaScript, while CommonJS modules is the default Node.js Module System

ES Modules is the standardized module system for JavaScript, while CommonJS modules is the default Node.js Module System

ES Modules use import and export, CommonJS use require() and module.export, both have different syntax.

Question 27

What kind of modules can Webpack support?

Answer 27

ECMAScript modules, CommonJS modules, and AMD modules.