JavaScript String Object

Original: JavaScript String Object

String Object 1. Introduced

String object that operates on a string, such as intercepting a substring, finding a string/character, converting a case, and so on.

2. Definition Method 2.1 new string (value) constructor: Returns a String object with content Value

Parameters:

①value {string}: String

return value:

{String Object} returns a String object with content value

Example:

var demostr = new String (' abc '); Console.log (typeof Demostr); = Objectconsole.log (DEMOSTR); = ABC

2.2 Direct Assignment (recommended)

Example:

var demostr = ' abc '; Console.log (typeof Demostr); Stringconsole.log (DEMOSTR); = ABC

3. Instance Property 3.1 Length: Returns the number of characters in a string

var s = ' abc '; Console.log (s.length); = = 3console.log (' Happy New Year '. length); + 4: A Chinese character is also calculated as 1 quantity console.log (". Length"); = 0: empty string returns 0

4. Example Methods

Note: The instance method of the string does not change the string itself, only returns the result after the operation.

4.1 charAt (Index): Returns the character at the specified position in a string, starting with the number 0, and returning an empty string if it passes in a value that does not exist

Parameters:

①index {int}: Position index, calculated starting from 0

return value:

{string} returns a character at the specified position in a string, and returns an empty string if it passes in a position value that does not exist

Example:

var s = ' abc '; Console.log (S.charat (1)); = = B: Returns the character of position 1 console.log (s); = = does not affect the original array console.log (S.charat (5)); = = ': Gets a character that does not exist and returns an empty string of length 0

4.2 charCodeAt (Index): Returns the Unicode encoding of the specified position character in a string

Parameters:

①index {int}: Position index, calculated starting from 0

return value:

{Number} returns the Unicode encoding of the specified position character in a string, and returns Nan if a nonexistent position value is passed in

Example:

var s = ' abc '; console.log (s.charcodeat (0)); = 98: Unicode encoding of Character B Console.log (S.charcodeat (5)); = = Nan: Gets a character that does not exist, returns Nan

4.3 concat (Value1,value2 ... valuen): concatenate one or more strings and return the concatenated string

Parameters:

①value1,value2. Valuen {string}: one or more strings

return value:

{string} returns the concatenated string

Example:

var s = ' abc '; Console.log (S.concat (' d ')); = Abcdconsole.log (s); = = ABC: does not affect the original string Console.log (S.concat (' d ', ' e ')); = ABCDE

4.4 IndexOf (value, |startposition): Finds a string or character in the previous instance, and returns the location found (counting from 0). If not found, return-1

Parameters:

①value {string}: String to find

②startposition {int} optional: Starting at the beginning of the lookup, starting from position 0 by default

return value:

{int} returns the location found (counting starting at 0). If not found, return-1

Example:

var s = ' abc '; Console.log (S.indexof (' B ')); = = 1console.log (S.indexof (' d ')); = 1: Console.log not Found (S.indexof (' B ', 2)); +-1: Starting at position 2 (3rd character) find

4.5 lastIndexOf (value, |startposition): Finds a string or character in the instance from the back to the beginning, and returns the location found (counting from 0). If not found, return-1

Parameters:

①value {string}: String to find

②startposition {int} optional: Starting from where to find, default from last

return value:

{int} returns the location found (counting starting at 0). If not found, return-1

Example:

var s = ' abcabc '; Console.log (S.lastindexof (' a ')); + 3: Look forward to Console.log (S.lastindexof (' d ')); = 1: No Return -1console.log (S.lastindexof (' A ', 2) found); + 0: Start looking forward from position 2 (3rd character)

4.6 Localecompare (value): instance compares with parameters, returns comparison results

Parameters:

①value {string}: string to be compared

return value:

0: larger instance than parameter

1: instance is equal to parameter

-1: Smaller instances than parameters

Example:

var s= ' abc '; Console.log (s.localecompare (' ab ')); + 1: the instance is larger than the parameter Console.log (S.localecompare (' abc ')); + 0: Instance and parameter Equal Console.log (S.localecompare (' Abd ')); + = 1: instance is smaller than parameter

　　

4.7 Match (REGEXP): Use regular expressions for matching lookups

Parameters:

①regexp {regexp}: Regular expression, eg:/\d+/

return value:

Returns a different result depending on whether the regular expression has an attribute ' G ' or not, and returns {null} if no match is found:

The ① regular expression does not take the property ' G ', performs a match, returns a {single match} result object, and the object contains the following properties:

Array ordinal: Indicates the matching result, 0 matches the text, 1 is from the right 1th parenthesis match result, 2 is the second parenthesis, and so on

Index property: Indicates where the matching text begins at the matching source

Input property: Represents a matching source

② regular expression with the attribute ' G ', performs a global match, finds all matching objects of the string, returns a {string array}: The array element contains each matching object in a string, does not contain a string within the parentheses of the regular expression, and does not provide the index and input properties.

Example:

1. Single match var s = ' a1b2c3d4 '; var mc = S.match (/\d+/); = = Gets the result of the first regular match if (MC! = null) {    console.log (mc.index);//+ = 1: Match the result at the beginning of the matching source    console.log (mc.input)//= > a1b2c3d4: Matching source    console.log (mc[0]);//+ = 1: Get matching Results}//2. Global match var Mcarray = S.match (/\d+/g); = = gets all regular matched numbers if (mcarray! = null) {for    (var i = 0,len=mcarray.length; i < Len; i++) {        var mc=mcarray[i] ;        Console.log (MC); = = 1,2,3,4: Gets the match to the result    }}//3. Parentheses match s = ' a1b2c3d4 '; mc = S.match (/[a-z] ([1-9])/); = = Gets the result of the first regular match if (MC! = null) {    console.log (mc.index);//+ = 0: Match the result at the beginning of the matching source    console.log (mc.input)//= > a1b2c3d4: Match source    Console.log (mc[0]);//+ = A1: Sequence number 0 Indicates the result of the match    Console.log (mc[1]);//= 1 : Ordinal 1 indicates a sub-match result in the first parenthesis}

4.8 Replace (RegExp, REPLACESTR): Replaces a substring that matches a regular expression and returns the replaced string

Parameters:

①regexp {regexp}: Regular expression. eg:/\d+/

②replacestr {string | function}:

1) If the string, which represents the replacement string, is replaced by the string;

The $ character in the string has a special meaning:

$1,$2: A matching subkey representing a left-to-right parenthesis for ① arguments

$&: A subkey that represents the entire ① parameter match

$$: Dollar sign

2) If the function, indicating that each match result calls this function, the function's unique parameter is the matching result, and returns a replacement result.

return value:

{string} returns a substituted string

Example:

var oldstr = ' a1b2c3d4 ';//1. Regular matches to "all" numbers, replaced by: ', ' comma var newstr = oldstr.replace (/\d+/g, ', '); Console.log (NEWSTR); = = a,b,c,d,//2. Regular matches to "all" number, replaced by: match result + ', ' comma newstr = oldstr.replace (/\d+/g, ' $&, '); Console.log (NEWSTR); = = a1,b2,c3,d4,//3. Regular matches to "all" numbers, each matching result calls the function and returns the replaced result newstr = Oldstr.replace (/\d+/g, function (word) {    if ( Word% 2 = = 0) {        return ' even ';    }    return ' odd ';}); Console.log (NEWSTR); + a odd B even c odd D even

4.9 Search (RegExp): Returns the position of the first match to find the regular expression

Parameters:

①regexp {regexp}: Regular expression. eg:/\d+/

return value:

{int} returns the position of the first matching result; 1 if no match is found

Example:

Console.log (' ABCD '. Search (/\d+/)); -1: No digital console.log (' abcd1234 '. Search (/\d+/)) was found; + 4: Position ordinal is 4, returns the position of the first digit

4.10 Slice (Start, |end): Returns a substring from the start position of the string to the previous position of end

Parameters:

①start {int}: The starting position index of the substring extraction (including the character at this location).

If the number is negative, the calculation starts at the end of the string. For example:-1 means the reciprocal of a string, and 2 represents the second-to-last character.

②end {int} optional: The end position index of the substring extraction (excluding characters at this location).

If the number is negative, the calculation starts at the end of the string. For example:-1 means the reciprocal of a string, and 2 represents the second-to-last character.

If this argument is omitted, all characters from the start position to the end are returned.

Attention:

The extraction order of the substring is left-to-right, and an empty string is returned if the start index position is greater than the end index position.

return value:

{string} returns a substring from the start position of the string to the previous position of end.

Example:

var s = ' ABCDEFG '; Console.log (S.slice (1)); BCDEFG: Omit end parameter, end position is end Console.log (S.slice (1, 3)); BC: Returns the substring Console.log (S.slice (-3)) from position ordinal 1 to position ordinal 2 (end previous position); EFG: Returns all characters Console.log (S.slice (-3,-1) from the third to the end of the countdown; EF: Returns all characters from the penultimate start to the second (end previous position)

4.11 Split (delimiter, |arraylength): Splits a string into an array of strings in a delimiter and returns

Parameters:

①delimiter {regexp | string}: The specified delimiter can be a regular expression or a string.

②arraylength {int} optional: The length of the split array. If omitted, all split substrings are returned.

Attention:

If the delimiter is in the first or last of the string, an empty string is added to the returned array.

return value:

{string[]} returns an array consisting of strings.

Example:

Console.log (' A,b,c,d,e '. Split (', ')); = = ["A", "B", "C", "D", "E"]console.log (', A,b,c,d,e, '. Split (', ') "); = = ["", "a", "B", "C", "D", "E", ""]: delimiter in the top or last side, an empty string Console.log (' a,b,c,d,e ') is added. Split (', ', 3)); = = ["A", "B", "C"]: Returns the first 3 split substring console.log (' a1b2c3d4e '. Split (/\d/)); = = ["A", "B", "C", "D", "E"]: Make a number as a delimiter

4.12 substr (Start, |wordlength): Returns a substring that is calculated from the start position of the string to a wordlength length

Parameters:

①start {int}: The starting position index of the substring extraction (including the character at this location).

If the number is negative, the calculation starts at the end of the string. For example:-1 means the reciprocal of a string, and 2 represents the second-to-last character.

②wordlength {int} optional: Extracts the length of the character. If this argument is omitted, all characters from the start position to the end are returned.

return value:

{string} returns the extracted string

Example:

Ar s = ' abcdefg '; Onsole.log (s.substr (0)); = =  ABCDEFG: Omit the second argument, return from position ordinal 0, one until the last character Onsole.log (s.substr (0, 3));//+ = ABC: Returns starting from position ordinal 0, Count of 3 characters Onsole.log (S.SUBSTR (2, 4)); = = Cdef: Returns starting from position ordinal 2, counting 4 characters Onsole.log (S.substr (-2, 3)); FG: Returns starting from the second-to-last string, counting 3 (more than the character length, returning only the statistical characters)

4.13 substring (start, |end): Returns a substring from the start position of the string to the previous position of end

Parameters:

①start {int}: The starting position index of the substring extraction (including the character at this location). Numbers cannot be negative, if negative number is treated as zero

②end {int} optional: The end position index of the substring extraction (excluding characters at this location). Numbers cannot be negative, if negative number is treated as zero

return value:

{string} returns a substring from the start position of the string to the previous position of end.

Example:

var s = ' ABCDEFG '; Console.log (s.substring (0)); = =  ABCDEFG: Omit the end parameter, return from position ordinal 0, until the last character Console.log (s.substring (0, 3));//= = ABC: returns from position ordinal 0 to position ordinal 2 ( The character of the previous ② parameter Console.log (s.substring (2, 4)); = = CD: Returns the character Console.log (S.substring (-3, 3) from the position ordinal 2 to the position ordinal 3 (the previous one of the ② parameters); ABC: If the parameter is negative, it is processed by the number zero, so this parameter actually returns the position ordinal 0 to the position ordinal 3 character

4.14 toUpperCase (): Converts a string to uppercase and returns 4.15 toLowerCase (): Converts the string to lowercase and returns 4.16 trim (): Removes the white space character at the beginning and end of the string and returns

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JavaScript String Object