From da78a9e329e272dedb2400b79a3bdeebff387d47 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:42:17 -0500 Subject: initial commit --- .../assertions/index.html" | 244 +++++++++++++++++++++ 1 file changed, 244 insertions(+) create mode 100644 "files/ko/web/javascript/guide/\354\240\225\352\267\234\354\213\235/assertions/index.html" (limited to 'files/ko/web/javascript/guide/정규식/assertions') diff --git "a/files/ko/web/javascript/guide/\354\240\225\352\267\234\354\213\235/assertions/index.html" "b/files/ko/web/javascript/guide/\354\240\225\352\267\234\354\213\235/assertions/index.html" new file mode 100644 index 0000000000..350c50f8f9 --- /dev/null +++ "b/files/ko/web/javascript/guide/\354\240\225\352\267\234\354\213\235/assertions/index.html" @@ -0,0 +1,244 @@ +--- +title: Assertions +slug: Web/JavaScript/Guide/정규식/Assertions +translation_of: Web/JavaScript/Guide/Regular_Expressions/Assertions +--- +

{{jsSidebar("JavaScript Guide")}}

+ +

Assertions에는 행이나 단어의 시작 · 끝을 나타내는 경계와 (앞, 뒤 읽고 조건식을 포함한) 어떤 식 으로든 매치가 가능한 것을 나타내는 다른 패턴이 포함됩니다.

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{{EmbedInteractiveExample("pages/js/regexp-assertions.html", "taller")}}
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Types

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Boundary-type assertions

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CharactersMeaning
^ +

Matches the beginning of input. If the multiline flag is set to true, also matches immediately after a line break character. For example, /^A/ does not match the "A" in "an A", but does match the first "A" in "An A".

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This character has a different meaning when it appears at the start of a group.

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$ +

Matches the end of input. If the multiline flag is set to true, also matches immediately before a line break character. For example, /t$/ does not match the "t" in "eater", but does match it in "eat".

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\b +

Matches a word boundary. This is the position where a word character is not followed or preceded by another word-character, such as between a letter and a space. Note that a matched word boundary is not included in the match. In other words, the length of a matched word boundary is zero.

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Examples:

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    +
  • /\bm/ matches the "m" in "moon".
    • +
  • /oo\b/ does not match the "oo" in "moon", because "oo" is followed by "n" which is a word character.
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  • /oon\b/ matches the "oon" in "moon", because "oon" is the end of the string, thus not followed by a word character.
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  • /\w\b\w/ will never match anything, because a word character can never be followed by both a non-word and a word character.
    • +
+ +

To match a backspace character ([\b]), see Character Classes.

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\B +

Matches a non-word boundary. This is a position where the previous and next character are of the same type: Either both must be words, or both must be non-words, for example between two letters or between two spaces. The beginning and end of a string are considered non-words. Same as the matched word boundary, the matched non-word boundary is also not included in the match. For example, /\Bon/ matches "on" in "at noon", and /ye\B/ matches "ye" in "possibly yesterday".

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+ +

Other assertions

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Note: The ? character may also be used as a quantifier.

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CharactersMeaning
x(?=y) +

Lookahead assertion: Matches "x" only if "x" is followed by "y". For example, /Jack(?=Sprat)/ matches "Jack" only if it is followed by "Sprat".
+ /Jack(?=Sprat|Frost)/ matches "Jack" only if it is followed by "Sprat" or "Frost". However, neither "Sprat" nor "Frost" is part of the match results.

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x(?!y) +

Negative lookahead assertion: Matches "x" only if "x" is not followed by "y". For example, /\d+(?!\.)/ matches a number only if it is not followed by a decimal point. /\d+(?!\.)/.exec('3.141') matches "141" but not "3.

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(?<=y)x +

Lookbehind assertion: Matches "x" only if "x" is preceded by "y". For example, /(?<=Jack)Sprat/ matches "Sprat" only if it is preceded by "Jack". /(?<=Jack|Tom)Sprat/ matches "Sprat" only if it is preceded by "Jack" or "Tom". However, neither "Jack" nor "Tom" is part of the match results.

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(?<!y)x +

Negative lookbehind assertion: Matches "x" only if "x" is not preceded by "y". For example, /(?<!-)\d+/ matches a number only if it is not preceded by a minus sign. /(?<!-)\d+/.exec('3') matches "3". /(?<!-)\d+/.exec('-3')  match is not found because the number is preceded by the minus sign.

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Examples

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General boundary-type overview example

+ +
// Using Regex boundaries to fix buggy string.
+buggyMultiline = `tey, ihe light-greon apple
+tangs on ihe greon traa`;
+
+// 1) Use ^ to fix the matching at the begining of the string, and right after newline.
+buggyMultiline = buggyMultiline.replace(/^t/gim,'h');
+console.log(1, buggyMultiline); // fix 'tey', 'tangs' => 'hey', 'hangs'. Avoid 'traa'.
+
+// 2) Use $ to fix matching at the end of the text.
+buggyMultiline = buggyMultiline.replace(/aa$/gim,'ee.');
+console.log(2, buggyMultiline); // fix  'traa' => 'tree'.
+
+// 3) Use \b to match characters right on border between a word and a space.
+buggyMultiline = buggyMultiline.replace(/\bi/gim,'t');
+console.log(3, buggyMultiline); // fix  'ihe' but does not touch 'light'.
+
+// 4) Use \B to match characters inside borders of an entity.
+fixedMultiline = buggyMultiline.replace(/\Bo/gim,'e');
+console.log(4, fixedMultiline); // fix  'greon' but does not touch 'on'.
+
+ +

Matching the beginning of an input using a ^ control character

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입력 시작시 일치를 위해 ^를 사용하십시오. 이 예에서는 /^A/ regex로 'A'로 시작하는 결과를 얻습니다. 여기서 ^는 한 가지 역할 만합니다. 적절한 결과를 보기위해 화살표 함수가있는 필터 메소드를 사용합니다.

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let fruits = ["Apple", "Watermelon", "Orange", "Avocado", "Strawberry"];
+
+// Select fruits started with 'A' by /^A/ Regex.
+// Here '^' control symbol used only in one role: Matching begining of an input.
+
+let fruitsStartsWithA = fruits.filter(fruit => /^A/.test(fruit));
+console.log(fruitsStartsWithA); // [ 'Apple', 'Avocado' ]
+
+ +

두 번째 예제에서 ^는 두 가지 모두에 사용됩니다 : 입력의 일치 시작점, 그룹에서 사용될 때 부정 또는 보완 문자 세트.

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let fruits = ["Apple", "Watermelon", "Orange", "Avocado", "Strawberry"];
+
+// Selecting fruits that dose not start by 'A' by a /^[^A]/ regex.
+// In this example, two meanings of '^' control symbol are represented:
+// 1) Matching begining of the input
+// 2) A negated or complemented character set: [^A]
+// That is, it matches anything that is not enclosed in the brackets.
+
+let fruitsStartsWithNotA = fruits.filter(fruit => /^[^A]/.test(fruit));
+
+console.log(fruitsStartsWithNotA); // [ 'Watermelon', 'Orange', 'Strawberry' ]
+ +

Matching a word boundary

+ +
let fruitsWithDescription = ["Red apple", "Orange orange", "Green Avocado"];
+
+// Select descriptions that contains 'en' or 'ed' words endings:
+let enEdSelection = fruitsWithDescription.filter(descr => /(en|ed)\b/.test(descr));
+
+console.log(enEdSelection); // [ 'Red apple', 'Green Avocado' ]
+ +

Lookahead assertion

+ +
// JS Lookahead assertion x(?=y)
+
+let regex = /First(?= test)/g;
+
+console.log('First test'.match(regex)); // [ 'First' ]
+console.log('First peach'.match(regex)); // null
+console.log('This is a First test in a year.'.match(regex)); // [ 'First' ]
+console.log('This is a First peach in a month.'.match(regex)); // null
+
+ +

Basic negative lookahead assertion

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For example, /\d+(?!\.)/ matches a number only if it is not followed by a decimal point. /\d+(?!\.)/.exec('3.141') matches "141" but not "3.

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console.log(/\d+(?!\.)/g.exec('3.141')); // [ '141', index: 2, input: '3.141' ]
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+ +

Different meaning of '?!' combination usage in Assertions and  Ranges 

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Different meaning of ?! combination usage in Assertions /x(?!y)/ and Ranges [^?!].

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let orangeNotLemon = "Do you want to have an orange? Yes, I do not want to have a lemon!";
+
+// Different meaning of '?!' combination usage in Assertions /x(?!y)/ and  Ranges /[^?!]/
+let selectNotLemonRegex = /[^?!]+have(?! a lemon)[^?!]+[?!]/gi
+console.log(orangeNotLemon.match(selectNotLemonRegex)); // [ 'Do you want to have an orange?' ]
+
+let selectNotOrangeRegex = /[^?!]+have(?! an orange)[^?!]+[?!]/gi
+console.log(orangeNotLemon.match(selectNotOrangeRegex)); // [ ' Yes, I do not want to have a lemon!' ]
+
+ +

Lookbehind assertion

+ +
let oranges = ['ripe orange A ', 'green orange B', 'ripe orange C',];
+
+let ripe_oranges = oranges.filter( fruit => fruit.match(/(?<=ripe )orange/));
+console.log(ripe_oranges); // [ 'ripe orange A ', 'ripe orange C' ]
+
+ +

Specifications

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SpecificationStatusComment
{{SpecName('ESDraft', '#sec-assertion', 'RegExp: Assertions')}}{{Spec2('ESDraft')}}
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Browser compatibility

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For browser compatibility information, check out the main Regular Expressions compatibility table.

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See also

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