JavaScript Scope

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

JavaScript Scope

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Scope is the set of variables you have access to.

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JavaScript Scope

자바스크립트에서 객체와 함수도 변수이다.

In JavaScript, scope is the set of variables, objects, and functions you have access to.

JavaScript has function scope: The scope changes inside functions.

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Local JavaScript Variables

Variables declared within a JavaScript function, become LOCAL to the function.

Local variables have local scope: They can only be accessed within the function.

함수 내에서만 사용가능

Example

// code here can not use carName

function myFunction() {
    var carName = "Volvo";

    // code here can use carName

}

Try it Yourself »

지역변수는 함수 내에서만 인식되기 때문에 ,  같은 이름의 변수를 다른 곳에서도 사용할 수 있다.

지역변수는 함수가 시작될 때 생성되고 함수가 끝날 때 삭제된다.

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Global JavaScript Variables

A variable declared outside a function, becomes GLOBAL.

A global variable has global scope: All scripts and functions on a web page can access it. 

전역변수 : 웹페이지의 모든 스크립트와 함수에서 사용가능

Example

var carName = " Volvo";

// code here can use carName

function myFunction() {

    // code here can use carName 

}

Try it Yourself »

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Automatically Global

If you assign a value to a variable that has not been declared, it will automatically become a GLOBAL variable.

This code example will declare carName as a global variable, even if it is executed inside a function.

사용자가 선언하지 않은 변수에 값을 할당할 경우 자동으로 전역변수가 되어

함수 내부에서도 사용되어도 전역변수처럼 사용된다..? 어렵.

Example

// code here can use carName

function myFunction() {
    carName = "Volvo";

    // code here can use carName

}

Try it Yourself »

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The Lifetime of JavaScript Variables

The lifetime of a JavaScript variable starts when it is declared.

함수실행이 완료되면 지역변수는 삭제된다.

전역 변수는 페이지를 닫을 때 삭제된다.

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Function Arguments

Function arguments (parameters) work as local variables inside functions.

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Global Variables in HTML

With JavaScript, the global scope is the complete JavaScript environment.

HTML에서 모든 전역변수는 window객체에 속한다.

Example

// code here can use window.carName

function myFunction() {
    carName = "Volvo";
}

Try it Yourself »

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Did You Know?

	Your global variables (or functions) can overwrite window variables (or functions). Any function, including the window object, can overwrite your global variables and functions.