JavaScript Syntax

http://www.w3schools.com/js/js_syntax.asp

JavaScript Syntax

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자바스크립트 작성 규칙

JavaScript Programs

A computer program is a list of "instructions" to be "executed" by the computer.

In a programming language, these program instructions are called statements.

JavaScript is a programming language.

자바스크립트 명령문은 ;(세미콜론)으로 구문된다.

Example

var x = 5;
var y = 6;
var z = x + y;

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	In HTML, JavaScript programs can be executed by the web browser.

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JavaScript Statements

JavaScript statements are composed of:

Values, Operators, Expressions, Keywords, and Comments.

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JavaScript Values

고정 값은 리터럴( literals)이라고합니다. 변수 값은 변수(variables)라고합니다.

JavaScript Literals

10.50

1001

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Strings are text, written within double or single quotes:

"John Doe"

'John Doe'

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JavaScript Variables

In a programming language, variables are used to store data values.

JavaScript uses the var keyword to declare variables.

An equal sign is used to assign values to variables.

In this example, x is defined as a variable. Then, x is assigned (given) the value 6:

var x;

x = 6;

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JavaScript Operators

JavaScript uses an assignment operator ( = , 대입연산자 ) to assign values to variables:

var x = 5;
var y = 6;

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JavaScript uses arithmetic operators ( + - *  /  , 산술연산자) to compute values:

(5 + 6) * 10

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JavaScript Expressions

An expression is a combination of values, variables, and operators, which computes to a value.

The computation is called an evaluation.

For example, 5 * 10 evaluates to 50:

5 * 10

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표현식은 변수 값을 포함 할 수 있습니다 :

x * 10

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값은 숫자 및 문자열 등 다양한 형태일 수 있다.

For example, "John" + " " + "Doe", evaluates to "John Doe":

"John" + " " + "Doe"

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JavaScript Keywords

JavaScript keywords are used to identify actions to be performed.

The var keyword tells the browser to create a new variable:

var x = 5 + 6;
var y = x * 10;

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JavaScript Comments

Not all JavaScript statements are "executed".

Code after double slashes // or between /* and */ is treated as a comment.

Comments are ignored, and will not be executed:

var x = 5;   // I will be executed

// var x = 6;   I will NOT be executed

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JavaScript Identifiers

Identifiers are names.

In JavaScript, identifiers are used to name variables (and keywords, and functions, and labels).

The rules for legal names are much the same in most programming languages.

In JavaScript, the first character must be a letter, an underscore (_), or a dollar sign ($).

Subsequent characters may be letters, digits, underscores, or dollar signs.

	숫자는 첫 번째 문자로 사용할 수 없다. 자바스크립트에서 첫번째문자는 문자, 밑줄 , 달러기호($) 여야 한다.

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JavaScript is Case Sensitive

자바스크립트는 대소문자 구분함.

The variables lastName and lastname, are two different variables.

lastName = "Doe";
lastname = "Peterson";

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JavaScript does not interpret VAR or Var as the keyword var.

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JavaScript and 카멜 케이스

변수명 결합시 사용법

Hyphens(-):

first-name, last-name, master-card, inter-city.

Underscore(_):

first_name, last_name, master_card, inter_city.

Camel Case:

FirstName, LastName, MasterCard, InterCity.

In programming languages, especially in JavaScript, camel case often starts with a lowercase letter:

firstName, lastName, masterCard, interCity.

	Hyphens are not allowed in JavaScript. It is reserved for subtractions.

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JavaScript Character Set

JavaScript uses the Unicode character set.

Unicode covers (almost) all the characters, punctuations, and symbols in the world.

For a closer look, please study our Complete Unicode Reference.