JavaScript string regexp regular expression related methods

Jintian 2020-11-12 23:19:35
javascript string regexp regular expression


Conceptual familiarity

The creation of regular expression objects

There are two main kinds of :
direct writing Literal amount of regular expression ,
Or use RegExp Construction method passed in Literal amount of regular expression .

Pay attention to the setting of the flag bit

r1 = /\d{3}/
/\d{
3}/
r2 = /\d{3}/gimy
/\d{
3}/gimy
r3 = new RegExp(/\d{3}/)
/\d{
3}/
r3 = new RegExp(/\d{3}/gimy)
/\d{
3}/gimy
r4 = new RegExp(/\d{3}/, "gimy")
/\d{
3}/gimy

The flag bit of a regular expression flags

g global Global mode
i ignoreCase Ignore case
m multiline Multi-line matching
y sticky Whether the search has “ viscosity ” see MDN RegExp sticky

More properties of regular expression objects

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String API

String.prototype.replace(searchValue, replaceValue): string

In this string : Appoint ( Mode ) character string Replace with replaceValue.
Returns a new result string .

Does not change the original string .
By default, only the first match is replaced , If the requirement is to replace it all , Set the regular expression global=true

example :

"123asd456hhh".replace(/\d/, "_"); // Replace the string with first Numeric character 
"_23asd456hhh"
"123asd456hhh".replace(/\d/g, "_"); // Replace the string with be-all Numeric character 
"___asd___hhh"

String.prototype.match(regexp): string[]

Find string str In the object , Specifies the substring of the pattern .
Returns an array of matched strings .

Still pay attention to flags

"123asd456hhh".match(/\d/)
["1", index: 0, input: "123asd456hhh", groups: undefined]
"123asd456hhh".match(/\d/g)
(6) ["1", "2", "3", "4", "5", "6"]

String.prototype.search(regexp): Number

To find the specified ( Mode ) Substring First occurrence ( Starting point subscript )
Returns the subscript value .

RegExp API

RegExp.prototype.test(string): boolean

Find... On a given string , Whether there are substrings that match the pattern .
If you want to test Whole string The pattern of , You can use regular expressions ^ $ Judge whether it's the beginning and the end .

/\d{3}/.test("123")
true
/\d{
3}/.test("123456")
true
/^\d{
3}$/.test("123456")
false

RegExp.prototype.compile(pattern, flag): RegExp

Recompile a regular expression .
because API The design is unreasonable , Have been abandoned .
see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp/compile

RegExp.prototype.exec(string): string[]

Perform a search on a given string , Search for substrings that match this pattern .
Returns an array of matching substrings .

See https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/RegExp/exec

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