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JavaScript手册
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RegExp
A regular expression object contains the pattern of a regular expression. It has properties and methods for using that regular expression to find and replace matches in strings.
In addition to the properties of an individual regular expression object that you create using the RegExp constructor function, the predefined RegExp object has static properties that are set whenever any regular expression is used.
创建源
A literal text format or the RegExp constructor function.
The literal format is used as follows:
/pattern/flags
The constructor function is used as follows:
new RegExp("pattern", "flags")
参数
Notice that the parameters to the literal format do not use quotation marks to indicate strings, while the parameters to the constructor function do use quotation marks. So the following expressions create the same regular expression:
/ab+c/i
new RegExp("ab+c", "i")
描述
When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary. For example, the following are equivalent:
re = new RegExp("\\w+")
re = /\w+/
表 4.3 provides a complete list and描述 of the special characters that can be used in regular expressions.
表 4.3 Special characters in regular expressions.
|
Character
|
Meaning
|
|---|
| \ | For characters that are usually treated literally, indicates that the next character is special and not to be interpreted literally. For example, /b/ matches the character 'b'. By placing a backslash in front of b, that is by using /\b/, the character becomes special to mean match a word boundary.-or-For characters that are usually treated specially, indicates that the next character is not special and should be interpreted literally. For example, * is a special character that means 0 or more occurrences of the preceding character should be matched; for example, /a*/ means match 0 or more a's. To match * literally, precede the it with a backslash; for example, /a\*/ matches 'a*'. | | ^ | Matches beginning of input or line.For example, /^A/ does not match the 'A' in "an A," but does match it in "An A." | | $ | Matches end of input or line.For example, /t$/ does not match the 't' in "eater", but does match it in "eat" | | * | Matches the preceding character 0 or more times.For example, /bo*/ matches 'boooo' in "A ghost booooed" and 'b' in "A bird warbled", but nothing in "A goat grunted". | | + | Matches the preceding character 1 or more times. Equivalent to {1,}.For example, /a+/ matches the 'a' in "candy" and all the a's in "caaaaaaandy." | | ? | Matches the preceding character 0 or 1 time.For example, /e?le?/ matches the 'el' in "angel" and the 'le' in "angle." | | . | (The decimal point) matches any single character except the newline character.For example, /.n/ matches 'an' and 'on' in "nay, an apple is on the tree", but not 'nay'. | | (x) | Matches 'x' and remembers the match.For example, /(foo)/ matches and remembers 'foo' in "foo bar." The matched substring can be recalled from the resulting array's elements [1], ..., [n], or from the predefined RegExp object's properties $1, ..., $9. | | x|y | Matches either 'x' or 'y'.For example, /green|red/ matches 'green' in "green apple" and 'red' in "red apple." | | {n} | Where n is a positive integer. Matches exactly n occurrences of the preceding character.For example, /a{2}/ doesn't match the 'a' in "candy," but it matches all of the a's in "caandy," and the first two a's in "caaandy." | | {n,} | Where n is a positive integer. Matches at least n occurrences of the preceding character.For example, /a{2,} doesn't match the 'a' in "candy", but matches all of the a's in "caandy" and in "caaaaaaandy." | | {n,m} | Where n and m are positive integers. Matches at least n and at most m occurrences of the preceding character.For example, /a{1,3}/ matches nothing in "cndy", the 'a' in "candy," the first two a's in "caandy," and the first three a's in "caaaaaaandy" Notice that when matching "caaaaaaandy", the match is "aaa", even though the original string had more a's in it. | | [xyz] | A character set. Matches any one of the enclosed characters. You can specify a range of characters by using a hyphen.For example, [abcd] is the same as [a-c]. They match the 'b' in "brisket" and the 'c' in "ache". | | [^xyz] | A negated or complemented character set. That is, it matches anything that is not enclosed in the brackets. You can specify a range of characters by using a hyphen.For example, [^abc] is the same as [^a-c]. They initially match 'r' in "brisket" and 'h' in "chop." | | [\b] | Matches a backspace. (Not to be confused with \b.) | | \b | Matches a word boundary, such as a space. (Not to be confused with [\b].)For example, /\bn\w/ matches the 'no' in "noonday";/\wy\b/ matches the 'ly' in "possibly yesterday." | | \B | Matches a non-word boundary.For example, /\w\Bn/ matches 'on' in "noonday", and /y\B\w/ matches 'ye' in "possibly yesterday." | | \cX | Where X is a control character. Matches a control character in a string.For example, /\cM/ matches control-M in a string. | | \d | Matches a digit character. Equivalent to [0-9].For example, /\d/ or /[0-9]/ matches '2' in "B2 is the suite number." | | \D | Matches any non-digit character. Equivalent to [^0-9].For example, /\D/ or /[^0-9]/ matches 'B' in "B2 is the suite number." | | \f | Matches a form-feed. | | \n | Matches a linefeed. | | \r | Matches a carriage return. | | \s | Matches a single white space character, including space, tab, form feed, line feed. Equivalent to [ \f\n\r\t\v].for example, /\s\w*/ matches ' bar' in "foo bar." | | \S | Matches a single character other than white space. Equivalent to [^ \f\n\r\t\v].For example, /\S/\w* matches 'foo' in "foo bar." | | \t | Matches a tab | | \v | Matches a vertical tab. | | \w | Matches any alphanumeric character including the underscore. Equivalent to [A-Za-z0-9_].For example, /\w/ matches 'a' in "apple," '5' in "$5.28," and '3' in "3D." | | \W | Matches any non-word character. Equivalent to [^A-Za-z0-9_].For example, /\W/ or /[^$A-Za-z0-9_]/ matches '%' in "50%." | | \n | Where n is a positive integer. A back reference to the last substring matching the n parenthetical in the regular expression (counting left parentheses).For example, /apple(,)\sorange\1/ matches 'apple, orange', in "apple, orange, cherry, peach." A more complete example follows this 表.Note: If the number of left parentheses is less than the number specified in \n, the \n is taken as an octal escape as described in the next row. | \ooctal
\xhex | Where \ooctal is an octal escape value or \xhex is a hexadecimal escape value. Allows you to embed ASCII codes into regular expressions. |
The literal notation provides compilation of the regular expression when the expression is evaluated. Use literal notation when the regular expression will remain constant. For example, if you use literal notation to construct a regular expression used in a loop, the regular expression won't be recompiled on each iteration.
The constructor of the regular expressionobject, for example, new RegExp("ab+c"), provides runtime compilation of the regular expression. Use the constructor function when you know the regular expression pattern will be changing, or you don't know the pattern and are getting it from another source, such as user input. Once you have a defined regular expression, and if the regular expression is used throughout the script and may change, you can use the compile method to compile a new regular expression for efficient reuse.
A separate predefined RegExp object is available in each window; that is, each separate thread of JavaScript execution gets its own RegExp object. Because each script runs to completion without interruption in a thread, this assures that different scripts do not overwrite values of the RegExp object.
The predefined RegExp object contains the static properties input, multiline, lastMatch, lastParen, leftContext, rightContext, and $1 through $9. The input and multiline properties can be preset. The values for the other static properties are set after execution of the exec and test methods of an individual regular expression object, and after execution of the match and replace methods of String.
属性概览
Note that several of the RegExp properties have both long and short (Perl-like) names. Both names always refer to the same value. Perl is the programming language from which JavaScript modeled its regular expressions.
方法概览
示例
示例 1. The following script uses the replace method to switch the words in the string. For the replacement text, the script uses the values of the $1 and $2 properties of the global RegExp object. Note that the RegExp object name is not be prepended to the $ properties when they are passed as the second argument to the replace method.
<SCRIPT LANGUAGE="JavaScript1.2">
re = /(\w+)\s(\w+)/;
str = "John Smith";
newstr=str.replace(re, "$2, $1");
document.write(newstr)
</SCRIPT>
This displays "Smith, John".
示例 2. In the following example, RegExp.input is set by the Change event. In the getInfo function, the exec method uses the value of RegExp.input as its argument. Note that RegExp is prepended to the $ properties.
<HTML>
<SCRIPT LANGUAGE="JavaScript1.2">
function getInfo() {
re = /(\w+)\s(\d+)/;
re.exec();
window.alert(RegExp.$1 + ", your age is " + RegExp.$2);
}
</SCRIPT>
Enter your first name and your age, and then press Enter.
<FORM>
<INPUT TYPE:"TEXT" NAME="NameAge" onChange="getInfo(this);">
</FORM>
</HTML>
属性
$1, ..., $9
Properties that contain parenthesized substring matches, if any.
描述
Because input is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.input.
The number of possible parenthesized substrings is unlimited, but the predefined RegExp object can only hold the last nine. You can access all parenthesized substrings through the returned array's indexes.
These properties can be used in the replacement text for the String.replace method. When used this way, do not prepend them with RegExp. The example below illustrates this. When parentheses are not included in the regular expression, the script interprets $n's literally (where n is a positive integer).
示例
The following script uses the replace method to switch the words in the string. For the replacement text, the script uses the values of the $1 and $2 properties of the global RegExp object. Note that the RegExp object name is not be prepended to the $ properties when they are passed as the second argument to the replace method.
<SCRIPT LANGUAGE="JavaScript1.2">
re = /(\w+)\s(\w+)/;
str = "John Smith";
newstr=str.replace(re, "$2, $1");
document.write(newstr)
</SCRIPT>
This displays "Smith, John".
$_
See input.
$*
See multiline.
$&
See lastMatch.
$+
See lastParen.
$`
See leftContext.
$'
See rightContext.
global
Whether or not the "g" flag is used with the regular expression.
描述
global is a property of an individual regular expression object.
The value of global is true if the "g" flag was used; otherwise, false. The "g" flag indicates that the regular expression should be tested against all possible matches in a string.
You cannot change this property directly. However, calling the compile method changes the value of this property.
ignoreCase
Whether or not the "i" flag is used with the regular expression.
描述
ignoreCase is a property of an individual regular expression object.
The value of ignoreCase is true if the "i" flag was used; otherwise, false. The "i" flag indicates that case should be ignored while attempting a match in a string.
You cannot change this property directly. However, calling the compile method changes the value of this property.
input
The string against which a regular expression is matched. $_ is another name for the same property.
描述
Because input is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.input.
If no string argument is provided to a regular expression's exec or test methods, and if RegExp.input has a value, its value is used as the argument to that method.
The script or the browser can preset the input property. If preset and if no string argument is explicitly provided, the value of input is used as the string argument to the exec or test methods of the regular expression object. input is set by the browser in the following cases:
- When an event handler is called for a TEXT form element, input is set to the value of the contained text.
- When an event handler is called for a TEXTAREA form element, input is set to the value of the contained text. Note that multiline is also set to true so that the match can be executed over the multiple lines of text.
- When an event handler is called for a SELECT form element, input is set to the value of the selected text.
- When an event handler is called for a Link object, input is set to the value of the text between <A HREF=...> and </A>.
The value of the input property is cleared after the event handler completes.
lastIndex
A read/write integer property that specifies the index at which to start the next match.
描述
lastIndex is a property of an individual regular expression object.
This property is set only if the regular expression used the "g" flag to indicate a global search. The following rules apply:
- If lastIndex is greater than the length of the string, regexp.test and regexp.exec fail, and lastIndex is set to 0.
- If lastIndex is equal to the length of the string and if the regular expression matches the empty string, then the regular expression matches input starting at lastIndex.
- If lastIndex is equal to the length of the string and if the regular expression does not match the empty string, then the regular expression mismatches input, and lastIndex is reset to 0.
- Otherwise, lastIndex is set to the next position following the most recent match.
For example, consider the following sequence of statements:
lastMatch
The last matched characters. $& is another name for the same property.
描述
Because lastMatch is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.lastMatch.
lastParen
The last parenthesized substring match, if any. $+ is another name for the same property.
描述
Because lastParen is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.lastParen.
leftContext
The substring preceding the most recent match. $` is another name for the same property.
描述
Because leftContext is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.leftContext.
multiline
Reflects whether or not to search in strings across multiple lines. $* is another name for the same property.
描述
Because multiline is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.multiline.
The value of multiline is true if multiple lines are searched, false if searches must stop at line breaks.
The script or the browser can preset the multiline property. When an event handler is called for a TEXTAREA form element, the browser sets multiline to true. multiline is cleared after the event handler completes. This means that, if you've preset multiline to true, it is reset to false after the execution of any event handler.
rightContext
The substring following the most recent match. $' is another name for the same property.
描述
Because rightContext is static, it is not a property of an individual regular expression object. Instead, you always use it as RegExp.rightContext.
source
A read-only property that contains the text of the pattern, excluding the forward slashes and "g" or "i" flags.
描述
source is a property of an individual regular expression object.
You cannot change this property directly. However, calling the compile method changes the value of this property.
方法
compile
Compiles a regular expression object during execution of a script.
语法
regexp.compile(pattern, flags)
参数
描述
Use the compile method to compile a regular expression created with the RegExp constructor function. This forces compilation of the regular expression once only which means the regular expression isn't compiled each time it is encountered. Use the compile method when you know the regular expression will remain constant (after getting its pattern) and will be used repeatedly throughout the script.
You can also use the compile method to change the regular expression during execution. For example, if the regular expression changes, you can use the compile method to recompile the object for more efficient repeated use.
Calling this method changes the value of the regular expression's source, global, and ignoreCase properties.
exec
Executes the search for a match in a specified string. Returns a result array.
语法
regexp.exec(str)
regexp(str)
参数
描述
As shown in the语法描述, a regular expression's exec method call be called either directly, (with regexp.exec(str)) or indirectly (with regexp(str)).
If you are executing a match simply to find true or false, use the test method or the String search method.
If the match succeeds, the exec method returns an array and updates properties of the regular expression object and the predefined regular expression object, RegExp. If the match fails, the exec method returns null.
Consider the following example:
<SCRIPT LANGUAGE="JavaScript1.2">
//Match one d followed by one or more b's followed by one d
//Remember matched b's and the following d
//Ignore case
myRe=/d(b+)(d)/ig;
myArray = myRe.exec("cdbBdbsbz");
</SCRIPT>
The following 表 shows the results for this script:
If your regular expression uses the "g" flag, you can use the exec method multiple times to find successive matches in the same string. When you do so, the search starts at the substring of str specified by the regular expression's lastIndex property. For example, assume you have this script:
<SCRIPT LANGUAGE="JavaScript1.2">
myRe=/ab*/g;
str = "abbcdefabh"
myArray = myRe.exec(str);
document.writeln("Found " + myArray[0] +
". Next match starts at " + myRe.lastIndex)
mySecondArray = myRe.exec(str);
document.writeln("Found " + mySecondArray[0] +
". Next match starts at " + myRe.lastIndex)
</SCRIPT>
This script displays the following text:
Found abb. Next match starts at 3
Found ab. Next match starts at 9
示例
In the following example, the user enters a name and the script executes a match against the input. It then cycles through the array to see if other names match the user's name.
This script assumes that first names of registered party attendees are preloaded into the array A, perhaps by gathering them from a party database.
<HTML>
<SCRIPT LANGUAGE="JavaScript1.2">
A = ["Frank", "Emily", "Jane", "Harry", "Nick", "Beth", "Rick",
"Terrence", "Carol", "Ann", "Terry", "Frank", "Alice", "Rick",
"Bill", "Tom", "Fiona", "Jane", "William", "Joan", "Beth"]
function lookup() {
firstName = /\w+/i();
if (!firstName)
window.alert (RegExp.input + " isn't a name!");
else {
count = 0;
for (i=0; i<A.length; i++)
if (firstName[0].toLowerCase() == A[i].toLowerCase()) count++;
if (count ==1)
midstring = " other has ";
else
midstring = " others have ";
window.alert ("Thanks, " + count + midstring + "the same name!")
}
}
</SCRIPT>
Enter your first name and then press Enter.
<FORM> <INPUT TYPE:"TEXT" NAME="FirstName" onChange="lookup(this);"> </FORM>
</HTML>
test
Executes the search for a match between a regular expression and a specified string. Returns true or false.
语法
regexp.test(str)
参数
描述
When you want to know whether a pattern is found in a string use the test method (similar to the String.search method); for more information (but slower execution) use the exec method (similar to the String.match method).
示例
The following example prints a message which depends on the success of the test:
function testinput(re, str){
if (re.test(str))
midstring = " contains ";
else
midstring = " does not contain ";
document.write (str + midstring + re.source);
}
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