IT 612
how do you access an element in an array?
with the index you wish to access inside the brackets alert ( greetings[0] );
can variables be overwritten?
yes
do template strings honor whitespace?
yes
are variables in javascript dynamically typed?
yes, meaning a variable can be an integer, and then later a string, then later an object, if so desired
are there predefined javascript objects?
yes, you can also define your own kind of objects
what is a JavaScript array?
"dynamic" entities that can change size after they are created
How do you concatenate in ES6?
Console.log(`Hello my name is ${firsName} ${lastName}. My age is ${age}.`);
what is an array?
Data structures consisting of related data items
Javascript Timeline 2003
ES4 abandoned (class, module, destructuring etc.)
Javascript Timeline 2009
ES5 (JSON, object methods, functional arrays etc.)
Javascript Timeline 2015
ES6 significant improvement(let, const, class, import, export etc.)
what is the DOM document object?
the root JavaScript object representing the entire HTML document
Javascript Timeline 1997
Standardized by ECMA
onload event
The most important event tells us an object is loaded and therefore ready to work with
what are the disadvantages of client-side scripting?
There is no guarantee that the client has JavaScript enabled What works in one browser, may generate an error in another web applications can be complicated to debug and maintain
how do you reduce validation errors?
Using pop-up JavaScript alert Provide textual hints to the user on the form itself Using tool tips to display context-sensitive help about the input a JavaScript-based mask
what does the cancelable property do?
a Boolean value that indicates whether or not the event can be cancelled
In the DOM, what is each element within the HTML document called?
a node
What is java script today like with node.js?
a real software language that's used to build full-stack applications
whats a constant?
a variable that cannot be overwritten Once declared, you cannot change its value
how do you find the length of a string in javascript?
alert (greet.length);
what does the math class do?
allows one to access common mathematic functions and common values quickly in one place
objects can also have methods, what are they?
are functions associated with an instance of an object
frame events
are the events related to the browser frame that contains your web page
what are some useful objects in javascript?
array, boolean, date, math, string
when can assignment happen?
at declaration-time by appending the value to the declaration, or at run time with a simple right-to-left assignment
how can many user input errors be eliminated?
by choosing a better data entry type than the standard
how are functions defined in javascript?
by using the reserved word function and then the function name and (optional) parameters
how do you access a single string charecter?
charAt()
what function shows a message on the console?
console.log("Message");
what can objects have associated with them?
constructors, properties, and methods
how do you display todays date as a string?
create a new object and use the toString() method var d = new Date();
==
equals (x==9) is true (x=="9") is true
===
exactly equals, including type (x==="9") is false (x===9) is true
Javascript Timeline 1996
first edition named Mocha/Live Script by Brendan Eich
when was react released?
in 1995 by Netscape, JavaScript has gone through many changes
what is a javascript event?
is an action that can be detected by JavaScript.
what does the bubble property do?
is set to true then there must be an event handler in place to handle the event or it will bubble up to its parent and trigger an event handler there
What is the DOM?
is the objects that make up a web page
<=, >=
les than or equal, greater than or equal (x<=9) is true
<,>
less than, greater than (x<5) is false
how do you declare variables with Es6?
let myName = "Ashley"; const myLastName = "Martin"; myLastName = "Smith" GIVES AN ERROR
what does the alert() function do?
makes the browser show a pop-up to the user, with whatever is passed being the message displayed
what methods does the math class contain?
max(), min(), pow(), sqrt(), and exp(), and trigonometric functions such as sin(), cos(), and arctan()
what are the event types?
mouse events keyboard events form events frame events
is java and javascript the same?
no java script and java are vastly different languages with different uses
are semi colons required?
no, but are permitted
are null and undefined the same states for a variable?
no, they are two distinctly different states
!=
not equal (4!=x) is true
!==
not equal in either value or type (x!=="0") is true (x!==9) is false
what are the advantages of client-side scripting?
process is on client not server, reducing load on server browser responds faster to user events can interact with html in a way the server cant
what is the scope of the let keyword?
protects the value of the global variable The value of the let variable is not reset outside of the if/else block
what does a template string do?
provide us with an alternative to string concatenation They also allow us to insert variables into a string Any JavaScript that returns a value can be added to a template string between the ${ } in a template string
types of input validation
required information correct data type correct format comparison range check custon
do functions require a return or parameter type?
since Javascript is dynamically typed, no
what does === mean?
tests not only for equality but type equivalence
how do you remove an item from the back of an array?
the pop method
what do you use to add an item to an existing array?
the push method greetings.push("Good Evening");
how does javascript interact with the HTML document?
through a programming interface (API) called the Document Object Model
what is the document.write() method used for?
to create output to the HTML page from JavaScript
how do you create a new object?
use the new keyword, the class name, and ( ) brackets with n optional parameters inside, comma delimited var someObject = new ObjectName(p1,p2,..., pn);
how can object properties be accessed?
using dot notation where a dot between the instance name and the property references that property alert(someObject.property);
how are methods called?
using the same dot notation as for properties, but instead of accessing a variable, we are calling a method someObject.doSomething();
how do you initialize an array with values?
var greetings = new Array("Good Morning", "Good Afternoon");
what code creates a new, empty array?
var greetings = new Array();