From da78a9e329e272dedb2400b79a3bdeebff387d47 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:42:17 -0500 Subject: initial commit --- .../reference/statements/with/index.html | 127 +++++++++++++++++++++ 1 file changed, 127 insertions(+) create mode 100644 files/ko/web/javascript/reference/statements/with/index.html (limited to 'files/ko/web/javascript/reference/statements/with/index.html') diff --git a/files/ko/web/javascript/reference/statements/with/index.html b/files/ko/web/javascript/reference/statements/with/index.html new file mode 100644 index 0000000000..30940cc297 --- /dev/null +++ b/files/ko/web/javascript/reference/statements/with/index.html @@ -0,0 +1,127 @@ +--- +title: with +slug: Web/JavaScript/Reference/Statements/with +translation_of: Web/JavaScript/Reference/Statements/with +--- +
Use of the with statement is not recommended, as it may be the source of confusing bugs and compatibility issues. See the "Ambiguity Contra" paragraph in the "Description" section below for details.
+ +
{{jsSidebar("Statements")}}
+ +

with statement 는 명령문의 범위 체인을 확장합니다.

+ +

Syntax

+ +
with (expression)
+  statement
+
+ +
+
expression
+
명령문을 평가할 때 사용되는 범위 체인에 지정된 표현식을 추가합니다. 표현식을 중괄호로 감싸는 것은 필수입니다.
+
statement
+
모든 구문을 말합니다. 여러개의 명령문을 실행하려면 블록명령문 ({...})을 사용하여 해당 명령문을 그룹화 하세요.
+
+ +

Description

+ +

JavaScript는 규정되지 않은 이름을 포함하는 스크립트 또는 함수의 실행 컨텍스트와 연관된 범위 체인을 검색하여 규정되지 않은 이름을 찾습니다. 'with'문은 해당 개체를 평가하는 동안 이 개체를 해당 범위 체인의 머리글에 추가합니다. 본문에 사용된 규정되지 않은 이름이 범위 체인의 속성과 일치하는 경우 이름은 속성과 속성이 포함 된 개체에 바인딩 됩니다. 그렇지 않으면, {{jsxref("ReferenceError")}} 가 발생됩니다.

+ +
with 를 사용하는 것은 권장하지 않으며, ECMAScript 5 strict mode에서는 금지되어 있습니다. 임시 변수에 액세스 하려는 속성이 있는 객체를 할당하는 것이 좋습니다.
+ +

Performance pro & contra

+ +

Pro: with 구문은 성능저하 없이 긴 객체 참조를 반복해야할 필요를 줄여서 파일 크기를 감소 시킬 수 있습니다. 'with'에 필요한 스코프 체인 변경은 연산 비용이 들지 않습니다. 'with'를 사용하면 반복되는 객체 참조를 파싱하는 인터프리터가 해소됩니다. 하지만 대게의 경우에 이 이점은 임시변수를 사용하여 원하는 객체에 대한 참조를 저장함으로써 얻을 수 있습니다.

+ +

Contra: The with statement forces the specified object to be searched first for all name lookups. Therefore all identifiers that aren't members of the specified object will be found more slowly in a 'with' block. Where performance is important, 'with' should only be used to encompass code blocks that access members of the specified object.

+ +

Ambiguity contra

+ +

Contra: The with statement makes it hard for a human reader or JavaScript compiler to decide whether an unqualified name will be found along the scope chain, and if so, in which object. So given this example:

+ +
function f(x, o) {
+  with (o) {
+    console.log(x);
+  }
+}
+ +

Only when f is called is x either found or not, and if found, either in o or (if no such property exists) in f's activation object, where x names the first formal argument. If you forget to define x in the object you pass as the second argument, or if there's some similar bug or confusion, you won't get an error -- just unexpected results.

+ +

Contra: Code using with may not be forward compatible, especially when used with something other than a plain object. Consider this example:

+ +
+
function f(foo, values) {
+  with (foo) {
+    console.log(values);
+  }
+}
+
+ +

If you call f([1,2,3], obj) in an ECMAScript 5 environment, then the values reference inside the with statement will resolve to obj. However, ECMAScript 6 introduces a values property on {{jsxref("Array.prototype")}} (so that it will be available on every array). So, in a JavaScript environment that supports ECMAScript 6, the values reference inside the with statement could resolve to [1,2,3].values. However, in this particular example, {{jsxref("Array.prototype")}} has been defined with values in its {{jsxref("Symbol.unscopables")}} object. If it were not, one can see how this would be a difficult issue to debug.

+
+ +

Examples

+ +

Using with

+ +

The following with statement specifies that the Math object is the default object. The statements following the with statement refer to the PI property and the cos and sin methods, without specifying an object. JavaScript assumes the Math object for these references.

+ +
var a, x, y;
+var r = 10;
+
+with (Math) {
+  a = PI * r * r;
+  x = r * cos(PI);
+  y = r * sin(PI / 2);
+}
+ +

Specifications

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('ESDraft', '#sec-with-statement', 'with statement')}}{{Spec2('ESDraft')}} 
{{SpecName('ES6', '#sec-with-statement', 'with statement')}}{{Spec2('ES6')}} 
{{SpecName('ES5.1', '#sec-12.10', 'with statement')}}{{Spec2('ES5.1')}}Now forbidden in strict mode.
{{SpecName('ES3', '#sec-12.10', 'with statement')}}{{Spec2('ES3')}} 
{{SpecName('ES1', '#sec-12.10', 'with statement')}}{{Spec2('ES1')}}Initial definition
+ +

Browser compatibility

+ + + +

{{Compat("javascript.statements.with")}}

+ +

See also

+ + -- cgit v1.2.3-54-g00ecf