Introduction to JavaScript

이 글은 JavaScript의 조건문이나 반복문 등 주요 개념을 배우기 전,
기본 문법 및 바탕이되는 개념사항들을 정리하기 위해 작성하였습니다.

 

 

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< Console >

A panel that displays important messages, like errors, for developers.

Data is printed, or logged, to the console withconsole.log()

 

ex)

console.log(22)   //   22

 

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< Comments >

To leave notes in our code for other developers or ourselves.

Computer will ignore it as our program runs.

 

• Single line comment  =>  Use  //
• Multi-line comment  => Use  /*  */

 

ex)

// Print 5 to the console
console.log(5);

/*
Print 5 to the console
please write "console.log(5);"
*/
console.log(5);

 

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< Data Types >

Data Types are the classifications we give to the different kinds of data that we use in programming.

In JavaScript, There are seven fundamental data types

 

• Number : Any number, including numbers with decimals  =>  ex) 4, 8, 15.16
• String : Any grouping of characters on your keyboard (letters, numbers, symbols, etc.) 
    =>  Use ' ... ' or " ... "
• Boolean : Only has two possible values  =>  true or false
• Null : This data type represents the intentional absence of a value  =>  represented by the keyword null
• Undefined : It also represents the absence of a value though it has a different use than null
    =>  denoted by the keyword undefined
• Symbol
• Object : Collectors of related data.

 

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< Arithmetic Operators >

• Add : +
• Subtract : -
• Multiply : *
• Divide : /
• Remainder : %

 

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< String Concatenation >

• 'A' + 'B' = 'AB'

 

ex)

'Hello ' + 'World!'   //   'Hello World!'

 

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< Properties >

To store data for an object

be called by the object or instance,  dot operator(.),  property

 

ex)

'hello'.length   //   5

 

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< Methods >

Actions we can perform.

be called by the object or instance,  dot operator(.),  property,  opening and closing parentheses

 

ex)

'hello'.toUpperCase()   //   'HELLO'

 

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< Built-in Object >

Collections of methods and properties that JavaScript provides

 

ex)

// Use Math object

console.log(Math.random());   //   prints a random number between 0 and 1
Math.floor(45.2);   //   45