web dev javascript polling q's

Javascript uses what type of typing, which determines variable type at runtime.

dynamic typing

Java script data types

string, array, bool, number

what would you expect this code to output?

true, false

what would you expect this to output?

510

what does console.log(array) do?

outputs array like

0: firstElement

1: secondElement

2: thirdElement

array.length

returns array length

for(let name of names) in javascript

for(string name: names) in c++

define a function named printValues with two parameters names and ages

function printValues(names, ages){}

do you need to declare function before you call it?

no

overloading javascript sort funtion

you can define and call an entirely new function within the .sort parentheses

define arrow function named add that adds a and b

let add=(a, b)=>(a+b);

how to add new items to an array

.push(“newName”)→ adds to the end, or unshift(“newName”) → adds it to the beginning

what is the standard for javascript

ECMAScript

Java vs. JavaScript

They are unrelated languages.

Running JavaScript

Runs inside either script tags or in an outside file. you can also type directly in the console

Executed by interpreter

JavaScript is interpreted line-by-line.

Semicolons in JavaScript

Optional but often used to end statements.

Special Values

NaN, null, and undefined.

Variables: let vs. const

`let` for changeable, `const` for fixed values.

Comments

// or /* */

Operators: === vs. ==

`===` checks type and value; `==` checks only value.

how to concatenate strings

+

String and Number Rules

Numbers convert to strings when concatonated

for each/for of loop

for(let char of string)

Functions

Named, anonymous, and arrow functions.

Local vs Global Scope

Local variables belong to functions, global to the program.

Default Parameters

function myFunction(defaultNum = 1)

Arrays

Declared with `[]`; access by index.

Array Method: length

Finds the number of elements.

Array Method: push()

Adds elements to the end.

Array Method: pop()

Removes the last element.

Array Method: sort()

Arranges elements in order.

Iterating Arrays

Use `for`, `for-of` loops.

Built-in Function: console.log()

Outputs messages to the console.

Built-in Function: parseInt()

Converts strings to integers.

Built-in Function: parseFloat()

Converts strings to floating-point numbers.

Built-in Function: isNaN()

Checks if a value is NaN.

Built-in Function: prompt()

Asks user for input.

define an object named object with an element1 named “Hello”

let object = {

element1: “Hello”,

}

Adding Object Properties

Use dot or bracket notation to add.

Object Methods

Define actions for objects; `this` refers to the object.

Accessors

Getters and setters control property behaviors.

Debugging

Use Chrome DevTools for debugging.

String Method: charAt()

Gets a character at a position.

String Method: indexOf()

Finds the position of a substring.

String Property: length

Finds string length.

String Templates

Use `` `${expression}` `` for dynamic strings.

what would this program output?

15, 3, 5, 9

how do you make an array nums be sorted in numerical order (as opposed to ascii order?)

nums.sort((a,b)=>a-b)— overloading the sorting function to sort in ascending order

what would you write to output denver broncos?

game.homeTeam.name

how to output Susan Cain?

book.authorFullName

set birthYear to 1985

book.author.birthYear = 1985;

what is s assigned?

a $a 5

What is missing from the if statement to count the number of spaces in string s?

s.charAt(i)=== “ “ or s[i] === ” “

how do you add a property to an object that already exists?

objectName[newProperty] = newProp;

what happens when you multiply a number by a string?

the string is converted to a number