20241120_1 기본

finds an HTML element       :      document.getElementById('demo')

 

Writing into an HTML element   :    innerHTML

Writing into the HTML output    :   document.write();

Writing into an alert box        :  window.alert(); or alert();

Writing into the browser console   :  console.log();

the browser to print the content of the current window  : window.print()

KeywordDescription

var	Declares a variable
let	Declares a block variable
const	Declares a block constant
if	Marks a block of statements to be executed on a condition
switch	Marks a block of statements to be executed in different cases
for	Marks a block of statements to be executed in a loop
function	Declares a function
return	Exits a function
try	Implements error handling to a block of statements

 

Hyphens are not allowed in JavaScript

Underscore, Upper Camel Case (Pascal Case), Lower Camel Case

 

The var keyword was used in all JavaScript code from 1995 to 2015.

The let and const keywords were added to JavaScript in 2015.

const if the value should not be changed

Block Scope(let) , Global Scope (var)

let

inside a { } block cannot be accessed from outside the block

can not be redeclared

var

inside a { } block can be accessed from outside the block

can be redeclared

	Scope	Redeclare	Reassign	Hoisted	Binds this
var	No	Yes	Yes	Yes	Yes
let	Yes	No	Yes	No	No
const	Yes	No	No	No	No

JavaScript Object(Objects, Properties, Methods, Display, Constructors)

create : ex) const person = {}; or const person = new Object();

add : ex)  person.nationalisy =  "";  

Accessing Object Properties

objectName.propertyName or objectName["propertyName"] 

nested Objects  : objectName["propertyName"] . ["propertyName1"] or objectName.propertyName.propertyName1

Deleting Properties

delete person.age; or delete person["age"];

Accessing Object Methods

objectName.methodName()

Adding a Method to an Object

person.name = function () {
  return this.firstName + " " + this.lastName;
};

 

 

 

http://www.w3schools.com 발췌