in JavaScript replace () Summary _javascript tips

About definitions

The replace () method replaces some characters in a string with some other characters, or replaces a substring that matches a regular expression.

About grammar

Stringobject.replace (regexp/substr,replacement)

About parameters

Parameters	Describe
Regexp/substr	Necessary. The RegExp object that prescribes the substring or pattern to be replaced. Note that if the value is a string, it is used as the direct text pattern to retrieve, not first converted to the RegExp object.
Replacement	Necessary. A string value. Provides a function that replaces text or generates alternate text.

1, the first parameter regexp/substr, the use of regular expressions with the global identifier G, you can replace all the matching substrings, otherwise it will only match once.

For example:

var str = "AAAAA"; 
var str1 = str.replace ("A", "B");
var str2 = str.replace (/a/g, "B");

Run Result: str1-> "Baaaa", str2-> "BBBBB"

2, the second parameter replacement, can be a string or function, can also be the specific meaning of the $ character.

character	Replace text
$, $ 、...、 $99	Text that matches the 1th to 99th subexpression in RegExp.
$&	The substring that matches the regexp.
$`	The text located on the left side of the matching substring.
$'	The text that is located to the right of the matching substring.
$$	The direct measure symbol.

A. Examples of function:

var str = "111222AA";
Str.replace (/(\d{3})/g, function (word) {return
 "B";
});

Run Result: "Bbaa"

Examples of B. $

var str = "1234567890";
Str.replace (/(\d{3}) (\d{3}) (\d{4})/g, "$1-$2-$3");

Run Result: "123-456-7890"

Note: Most of the time is to use the combination of regexp and $ to implement the requirements, so it is necessary to know some basic regular expression rules.

String substitution string

' I am loser! '. Replace (' Loser ', ' hero ')

I am hero!
Using strings directly allows you to turn from loser to hero, but if you have 2 loser, you can't turn hero together.

' I am loser,you are loser '. Replace (' Loser ', ' hero ');
I am Hero,you are loser

The regular expression is replaced with a string

' I am loser,you are loser '. Replace (/loser/g, ' hero ')
//i am Hero,you are

Using regular expressions and changing the regular global property to True allows all loser to become hero

Interesting substitution characters

Replacevalue can be a string. If there are several specific characters in the string, they are converted to a specific string.

Character replacement text
$& a string that matches a regular match
$ ' matches the character to the left of the string
$ ' matches the character to the right of the string
$1,$2,$,3,..., $n Matching results in matched results
Use $& characters to add braces to matching characters

var sstr= ' discusses the use of Replace in regular expressions ';
Sstr.replace (/Regular expression/, ' {$&} ');
Discuss the use of Replace in {regular expression}
Replace content with $ ' and $ ' characters

' ABC '. Replace (/b/, "$ '");
Aac
' ABC '. Replace (/b/, "$ '");
Acc
Combining a new string with a grouping match

' nimojs@126.com '. Replace (/(. +) (@) (. *)/, "$2$1")
//@nimojs
The Replacevalue parameter can be a function

The Replacevalue in Stringobject.replace (Searchvalue,replacevalue) can be a function.
If Replacevalue is a function, then the arguments of this function will have n+3 arguments (n is the number of matches to the regular)

See examples to help understand:

function logarguments () { 
 console.log (arguments);
["Nimojs@126.com", "Nimojs", "@", "126.com", 0, "nimojs@126.com"] 
 return ' Returns the value will replace the match to the target '
}
Console.log (
 ' nimojs@126.com '. Replace (/(. +) (@) (. *)/,logarguments)
)

Parameters are

Matching to the string (this example is nimojs@126.com, recommended to modify the code above the regular to see matching characters to help understand)
If you are using a group match for more than one, there is no such argument. (The argument for this example is "Nimojs", "@", "126.com".) Recommended modifications regular for/nimo/view the arguments value returned in the console)
Match the corresponding index position of the string (this example is 0)
Raw string (This example is nimojs@126.com)
Use a custom function to change the a-g string to lowercase

' JAVASCRIPT '. Replace (/[a-g]/g,function () {return
 arguments[0].tolowercase ();
})
Javascript

Use custom functions to make callback substitutions to remove single quotes from inline styles

' <span style= ' font-family:\ ' Microsoft Ya Black '; >demo</span> '. Replace (/\ ' [^ ']+\ '/g,function () {  
 var sresult=arguments[0];
 Console.log (Sresult)//' Microsoft Ya-black '
 sresult=sresult.replace (/\ '/g, ');
 Console.log (sresult);
Microsoft ya
-
black return sresult;} <span style= "font-family: Microsoft James Black;" >demo</span>