JS Replace how to implement ReplaceAll

JS under the String object's replace method is defined as follows:

Stringobject.replace (regexp/substr,replacement)

which

Parameters | Describe

Regexp/substr | Necessary. A RegExp object that specifies the substring or pattern to replace.

Replacement | Necessary. A string value. A function that specifies replacement text or generates alternate text.

return value

A new string that is obtained after the first match or all matches of regexp have been replaced with replacement .

Description

The replace () method of the string Stringobject performs a find-and-replace operation. It looks for substrings in Stringobject that match regexp, and then replaces them with replacement . If RegExp has global flag G, then the Replace () method replaces all matching substrings. Otherwise, it replaces only the first matched substring.

replacement can be a string, or it can be a function. If it is a string, then each match is replaced by a string. However, the $ character in replacement has a specific meaning. As shown in the following table, it shows that the resulting string from a pattern match will be used for substitution.

Characters | Replace text

$, $ 、...、 | The text that matches the 1th to 99th sub-expression in RegExp.

$& | A substring that matches the regexp.

$ ' (The one above the TAB key) | The text that is located to the left of the matching substring.

$ ' | The text on the right side of the matching substring.

$$ | Direct volume symbol.

Note: ECMAScript v3 stipulates that the parameter replacement of the replace () method can be a function instead of a string. In this case, each match calls the function, and the string it returns is used as the replacement text. The first parameter of the function is a string that matches the pattern. The next parameter is a string that matches the subexpression in the pattern and can have 0 or more of these parameters. The next argument is an integer that declares where the match appears in the Stringobject. The last parameter is the stringobject itself.

Above is a description of the w3school above for the string object replace method. Let's look at the test:

var str = ' BbBb '; Console.log (str.replace (' B ', ' B '));

At this point the console will print: ' BbBb ' instead of ' bbBb '.

That is, when the argument ' Regexp/substr ' is a string, only the first matched substring is replaced. The JS string object does not provide a ReplaceAll method, so you can only try another method, the parameter ' Regexp/substr ' is a regular Expression object--regexp object.

Let's take a look at what the RegExp object (which has been understood to skip directly), and here's how the RegExp object is created:

Direct Volume Syntax:

/pattern/attributes

Syntax for creating RegExp objects:

New REGEXP (pattern, attributes);

Parameters

Parameter pattern is a string that specifies the pattern of a regular expression or other regular expression.

The parameter attributes is an optional string that contains the property "G", "I", and "M", respectively, for specifying global matching, case-sensitive matching, and multiline matching. The M attribute is not supported until ECMAScript is normalized. If pattern is a regular expression, not a string, you must omit the parameter.

return value

A new RegExp object that has the specified pattern and flags. If the parameter pattern is a regular expression instead of a string, the RegExp () constructor creates a new RegExp object with the same pattern and flags as the specified REGEXP.

Without the new operator, and REGEXP () as a function call, it behaves as if it were called with the new operator, except that when pattern is a regular expression, it only returns pattern, and no longer creates a new The RegExp object.

Thrown

SyntaxError-Throws the exception if pattern is not a valid regular expression, or if the attributes contains characters other than "G", "I", and "M".

TypeError-Throws the exception if pattern is a RegExp object but does not omit the attributes parameter.

Use the RegExp object to test the above example:

var str = ' BbBb '; Console.log (str.replace(new RegExp (' B '), ' B '));

The result is: ' bbBb ', or only the first matched substring is replaced. Let's take a look at the description of the second parameter of the RegExp constructor object:

Modifier | Describe

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.

As you can see from above, when the second argument string contains the character ' G ', a global match is made. Let's Test it here:

var str = ' BbBb '; Console.log (str.replace (New

At this point the print: ' bbbb '. This is the result we want.

Of course, creating regexp objects above can also be used in direct volume.

New REGEXP (' b ')  = =/b/new RegExp (' B ', ' g ') = =/b/g

By the way, look at the case insensitive match, used with the global match:

var str = ' BbBb '; Console.log (Str.replace (/b/gi, ' a '));

This will print: ' AAAA '.

In fact, the key is in the use of regular expressions. Attach the W3school above RegExp object Description: http://www.w3school.com.cn/jsref/jsref_obj_regexp.asp

JS Replace how to implement ReplaceAll