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Regular expressions, also known as regular expressions. (English: Regular Expression, often abbreviated as regex, RegExp, or re in code)
Create a RegExp objectThe RegExp object is used to store the retrieval mode.
Methods for REGEXP objectsvar patt1=new RegExp("e"，"g");//创建对象定义，检索模式为e（查找e这个字符）var patt1=/e/g;//直接量定义，检索模式为e（查找e这个字符）
The RegExp object has 3 methods: Test (), exec (), and compile ().
Test (): Retrieves the specified value in the string. The return value is the value that was found. If no match is found, NULL is returned.
EXEC (): Retrieves the specified value in the string. The return value is the value that was found. If no match is found, NULL is returned. (exec stores the matched bits on a global match, and executes again from the stored position)
Compile (): Changing the retrieval mode of RegExp
//先查找e，再查找d。因为这个字符串中存在e，不存在d所以返回truefalse//查找evar patt1=new RegExp("e");document.write(patt1.test("The best things in life are free"));//查找dpatt1.compile("d");document.write(patt1.test("The best things in life are free"));| Properties | Description | FF | IE |
|---|---|---|---|
| Global | RegExp whether the object has a flag g. | 1 | 4 |
| IgnoreCase | RegExp whether the object has a flag I. | 1 | 4 |
| LastIndex | An integer that indicates the character position at which to start the next match. | 1 | 4 |
| Multiline | RegExp whether the object has a flag m. | 1 | 4 |
| Source | The source text of the regular expression. | 1 | 4 |
| Method | Description | FF | IE |
|---|---|---|---|
| Search | Retrieves a value that matches a regular expression. | 1 | 4 |
| Match | Finds a match for one or more regular expressions. | 1 | 4 |
| Replace | Replace the substring that matches the regular expression. | 1 | 4 |
| Split | Splits a string into an array of strings. | 1 | 4 |
| modifier | Description |
|---|---|
| I | Performs a match that is not case sensitive. |
| G | Performs a global match (finds all matches rather than stops after the first match is found). |
| M | Performs multi-line matching. |
| An expression | Description |
|---|---|
| [ABC] | Look for any characters between square brackets. |
| [^ABC] | Look for any characters that are not in square brackets. |
| [0-9] | Look for any number from 0 to 9. |
| [A-z] | Finds any characters from a to lowercase z from a small write. |
| [A-z] | Look for any characters from uppercase A to uppercase Z. |
| [A-z] | Look for any characters from uppercase A to lowercase z. |
| [ADGK] | Finds any character within a given collection. |
| [^ADGK] | Finds any character outside the given collection. |
| (Red|blue|green) | Finds any of the specified options. |
| Meta character | Description |
|---|---|
| . | Finds a single character, in addition to line breaks and line terminators. |
| \w | Find the word character. |
| \w | Finds non-word characters. |
| \d | Find numbers. |
| \d | Finds non-numeric characters. |
| \s | Find white space characters. |
| \s | Finds non-whitespace characters. |
| \b | Matches the word boundary. |
| \b | Matches a non-word boundary. |
| / | Find NUL characters. |
| \ n | Find line breaks. |
| \f | Find a page break. |
| \ r | Look for the carriage return character. |
| \ t | Find tabs. |
| \v | Find vertical tabs. |
| \xxx | Find the characters that are specified in octal number XXX. |
| \xdd | Finds the characters specified in hexadecimal number DD. |
| \uxxxx | Finds the Unicode characters specified in hexadecimal number xxxx. |
| quantifier | Description |
|---|---|
| n+ | Matches any string that contains at least one n. |
| N | Matches any string that contains 0 or more N. |
| N? | Matches any string that contains 0 or one n. |
| N{X} | Matches a string that contains a sequence of X N. |
| N{x,y} | Matches a string containing a sequence of X to Y N. |
| N{x,} | Matches a string that contains at least X N of a sequence. |
| n$ | Matches any string that ends with N. |
| ^n | Matches any string that begins with N. |
| Capture | Description |
|---|---|
| (x) | Match ' X ' and remember the match. |
| (?: x) | Matches the specified string x but does not remember the match (the parentheses are not used as an item in the result array). |
Pre-check<!DOCTYPE html><script>var test = ‘this are some test text‘;console.log(test.match(/(te)(?:st)/));//[ ‘test‘, ‘te‘, index: 14, input: ‘this are some test text‘ ]//(te)被捕捉了（结果数组第二项：test中的te被捕获），(?:st)没有被捕捉（结果数组中没有）//</script>
| Pre-check | Description |
| (? =x) | Matches any string immediately after the specified string x (positive lookup). |
| (?! X) | Matches any string that is not followed by the specified string x (forward negation lookup). |
Looks like ES7 to support reverse pre-check , first use parentheses instead of it
<!DOCTYPE html><script>var test = ‘this are some test text‘;console.log(test.match(/te(st.*)/));console.log(‘反向预查：‘+test.match(/te(st.*)/)[1]);/*[ ‘test text‘, ‘st text‘, index: 14, input: ‘this are some test text‘ ]反向预查：st text*/</script>
Positive pre-check usage: pre-check the end of the conditions, pre-check the conditions are not included in the matching results, pre-check conditions do not affect the current matching position pointer
Eg: Find out all the
<!DOCTYPE html>
Match Results
Properties
meaning
$1...$9
If it (s) exists, is the substring that matches to
$_
The string that is matched
$*
Whether to make multi-line matching (bool type)
$&
Last-match Index
$+
The last substring enclosed in parentheses
$`
Last match with left substring
$
Last match with right substring
var test = ‘this are some test text‘;document.write(test.replace(/(this).*?(text)/, "\$1 = $1,\$2 = $2,\$_ = $_,\$* = $*,\$& = $&,\$+ = $+,\$` = $`,\$‘ = $‘"));
JS Regular expression
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