mode 4 JS II

Question 1

What is an array?

Answer 1

• a group of data entries

- Each data entry has an index associated with it. indeces begin with (0) to (arraySize -1)

Question 2

how do we declare an array?

how do you see all the contents of an array?

how do you obtain the length of the array (the # of elements)?

how do you access elements in an array?

Answer 2

how do we declare an array?
var arrayOne= ['Billy', 'Katherine'];
// remember, JS is loosely typed
var arrayTwo= ['Billy', 'Katherine', 77, false];
//                             0           1         2    3

// how do you see all the contents of an array?
console.log(arrayTwo);

// how do you obtain the length of the array (the # of elements)?
//console.log(arrayTwo.length); // prints "4"

// how do you access elements in an array?
//console.log(arrayTwo[0]); // prints "Billy"

Question 3

what if you attempt to access an element that doesn’t exist?

what if you attempt to update an element that doesn’t exist?

how do I dynamically remove elements from an array?

Answer 3

//what if you attempt to access an element that doesn't exist?
var arrayOne= ['Billy', 'Katherine'];
// remember, JS is loosely typed
var arrayTwo= ['Billy', 'Katherine', 77, false];
//                             0           1         2    3

console.log(arrayTwo[50]); //prints “undefined”

//what if you attempt to update an element that doesn't exist?
arrayTwo[6]="does this work?";
// console.log(arrayTwo);
// console.log(arrayTwo[5]); //prints "undefined"
// console.log(arrayTwo[6]); //prints "does this work?"

//how do I dynamically remove elements from an array?
var arrayDelete = [6, 8, 10, 12];
delete arrayDelete[1];
console.log(arrayDelete); 
console.log(arrayDelete[1]); //prints "undefined"

Question 4

What is an object?

Answer 4

• a model of a real world physical object
  - it has state and behavior
  - in JS, objects are key-value pairs

Question 5

how do I create an object?

Answer 5

var objectOne = {
    // to declare a member of an object, you use key-value pairs
    // attribute: value

name: "Danny Boy",
'ability': 'electromagnetism',
'official bounty': 250000,

    // this is how you'd add a method
    doCrimeMethod: function(){
        // method logic
        console.log("inside doCrimeMethod()")
    }
}

Question 6

What is a function?

Answer 6

• a reusable block of code
  
  • it performs some service for the rest of the application
  (Note: function vs method. A method is just a function that is attached to an object)

Question 7

What is the different between an argument and a parameter?

Answer 7

• parameters are used to declare WHICH variables a function/method will use.
  
  • arguments are the actual values passed into a function/method as it is invoked

Question 8

how do I declare a function?

Answer 8

function myFunction(){}

//I can also give a function parameters
var myFunctionTwo = function (lePokemans, leMoveSet){
console.log(“The objective best pokemon is: “+lePokemans);
console.log(leMoveSet);

Question 9

What is control flow?

Answer 9

• control flow are a series of functionalities that allow the developers to alter the logical flow of the application
  
  • normally in an application lines of logic are read top to bottom. Using control flow we can alter the way the lines of logic are ready. We can make lines of code repeat or even be skipped

Question 10

Keywords associated with control flow?

Answer 10

• if, else if, else
  
  • while, for, do-while, foreach
  • switch
  • break, continue
  • ”?” and the ternary operator

Question 11

What are the TRUTHY values in JS?

Answer 11

Anything that isn’t a FALSEY value

Question 12

What are the FALSEY values in JS?

Answer 12

false, 0, “”, null, NaN, undefined

Question 13

Short-circuiting

Answer 13

Short circuiting

T and T     =   T
T and F     =   F
F and T     =   F
F and F     =   F

T or T     =   T
T or F     =   T
F or T     =   T
F or F     =   F

shortcircuiting operators:   &&  , ||
bitwise operators:   & , |,  ^, etc

Question 14

What is a string?

Answer 14

a primitive datatype in JS

it represents a series of characters

Question 15

how do I create a string?

Answer 15

var name= ‘Billy “The Warden”’;

Question 16

COMPLEX STRINGS

Answer 16

backtiks aka template literals will evaluate an expression with ${}

Question 17

What is ECMAScript

Answer 17

ECMAScript is a standardization of functionalities that scripting languages should have.
Various versions of ECMAScript add different functionalities.
e.g. it can be denoted like “ES6” or “ES2015” or “ECMAScript2015”

Question 18

Why do we use “use strict”;

Answer 18

-“use strict” is used to stop devs from declaring variables WITHOUT using “let” or “const” or “var”

“use strict”;