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javascript之RegExp
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.
| Core object | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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
| pattern | The text of the regular expression. |
| flags | (Optional) If specified, flags can have one of the following 3 values: |
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 = newRegExp("\\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 4.3Special characters in regular expressions.
The constructor of the regular expressionobject, for example, newRegExp("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 thecompile method to compile a new regular expression for efficient reuse.
The predefined RegExp object contains the static properties input, multiline, lastMatch, lastParen, leftContext, rightContext, and $1 through $9. Theinput and multiline properties can be preset. The values for the other static properties are set after execution of theexec and test methods of an individual regular expression object, and after execution of thematch 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
| compile | Compiles a regular expression object. |
| exec | Executes a search for a match in its string parameter. |
| test | Tests for a match in its string parameter. |
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".
<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.
| 属性源 | RegExp |
| 静态, 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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 theString.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.
| 属性源 | RegExp |
| 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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 thecompile method changes the value of this property.
ignoreCase
Whether or not the "i" flag is used with the regular expression.
| 属性源 | RegExp |
| 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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 thecompile method changes the value of this property.
input
The string against which a regular expression is matched. $_ is another name for the same property.
| 属性源 | RegExp |
| 静态 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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.
- 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>.
lastIndex
A read/write integer property that specifies the index at which to start the next match.
| 属性源 | RegExp |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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.
lastMatch
The last matched characters. $& is another name for the same property.
| 属性源 | RegExp |
| 静态, 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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.
| 属性源 | RegExp |
| 静态, 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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.
| 属性源 | RegExp |
| 静态, 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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.
| 属性源 | RegExp |
| 静态 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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.
rightContext
The substring following the most recent match. $' is another name for the same property.
| 属性源 | RegExp |
| 静态, 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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.
| 属性源 | RegExp |
| 只读 | |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
描述
source is a property of an individual regular expression object.You cannot change this property directly. However, calling thecompile method changes the value of this property.
方法
compile
Compiles a regular expression object during execution of a script.
| 方法源 | RegExp |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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'ssource, global, and ignoreCase properties.
exec
Executes the search for a match in a specified string. Returns a result array.
| 方法源 | RegExp |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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 thetest method or the String search method.
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:
<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.
| 方法源 | RegExp |
| 实现版本 | Navigator 4.0, Netscape Server 3.0 |
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 theString.search method); for more information (but slower execution) use theexec 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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