Java Script

Question 1

What is a switch statement?

Answer 1

switch checks the variable for a comparison match on each case. They use strict equality Switch(varible){ case ‘A’ : ‘code to run’ break; case ‘B’: case ‘C’: default: ‘default case only runs if all other cases don’t match. }

Question 2

What is block scope?

Answer 2

when the hierarchy with a block some method { inside, the bracket is a block of code. }

Question 3

What is Global scope?

Answer 3

Global scope is the scope defined by the entire document. I.e the file is a block of code.

Question 4

Should you use var to define a varible

Answer 4

Normally no. use let or const as they are defined by block scope.

Question 5

function expression

Answer 5

function (){ does something };

expressions always have semicolons at the end!

Question 6

How do create a function expression.

Answer 6

const name = function() { does something };

Has a semi colon at the end.

Function Expression is used inside the statement: let sayHi = …;, as a value. It’s not a code block, but rather an assignment. The semicolon ; is recommended at the end of statements, no matter what the value is. So the semicolon here is not related to the Function Expression itself, it just terminates the statement.

Question 7

What is hoisting

Answer 7

Hoisting is JavaScript’s default behaviour of moving declarations to the top. a variable can be declared after it has been used variables defined with let and const are hoisted to the top of the block, but not initialized.

Question 8

What does hoisting not do.

Answer 8

JavaScript only hoists declarations, not initializations.

Question 9

Upon on the use of this. what does this refer to? return this.firstName + “ “ + this.lastName;

Answer 9

M - Method, this refers to the owner object. - M* - Methods like call(), and apply() can refer this to any object. A - Alone, this refers to the global object. F - In a function, this refers to the global object. - F* - In a function, in strict mode, this is undefined. E - Event, this refers to the element that received the event.

Question 10

What is the global object

Answer 10

in a browser: it is the object [object Window]:

Question 11

What is an expression in javascript

Answer 11

+ long a winded need to come back to

Question 12

What is an argument in a function

Answer 12

it is the argument that is parsed let firstFucntion = function(parameter) { do something } firstFunction(‘hello’) – ‘hello’ is the argument

Question 13

What is a parameter in a function?

Answer 13

it is the variable that is defined to have arguments parsed into it. let firstFucntion = function(parameter) { do something } firstFunction(‘hello’) – ‘hello’ is the argument

Question 14

what do default values doe in a function

Answer 14

they assign values to the parameters if there are no arguments provided.

Question 15

how do you create an arrow function?

Answer 15

const firstFunction = (prameter1, parameter 2 ) => { return something ; }; note if there is only one function and no need for return const firstFuntion = pramerter => something;

Question 16

Difference between methods vs functions

Answer 16

methods invoke dot notation. they are invoked on an object or datatype e.g object.method()

Question 17

what is a call back function

Answer 17

is any executable code that is passed as an argument to other code; that other code is expected to call back (execute) the argument at a given time. This execution may be immediate as in a synchronous callback, or it might happen at a later time as in an asynchronous callback. Programming languages support callbacks in different ways, often implementing them with subroutines, lambda expressions, blocks, or function pointers

Question 18

what does forEach do

Answer 18

The forEach() method calls a function once for each element in an array, in order. takes 2 parameters, ( parameter, index )

Question 19

How do you do complex mathematical things in java script

Answer 19

Use the Math object that is built into java script

Question 20

What is a reference type

Answer 20

a reference type is

• Object literals
• Arrays
• functions
• Dates
  *

Question 21

What is a primitive type?

Answer 21

primitatve types are

• numbers
• strings
• booleans
• null
• undefined
• symbols

stored on the stack

Question 22

what is a reference type?

Answer 22

it is sat on the heap

• object literals
• Functions
• dates
• an

Question 23

what is the spread operator?

Answer 23

The spread syntax can be used when all elements from an object or array need to be included in a list of some kind. indicated by 3 dots

….

example

let numberStore = [0, 1, 2];

let newNumber = 12;

numberStore = […numberStore, newNumber];