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1. String.fromCodePoint()

The first thing to mention is that string.fromCharCode (), both methods are used to convert Unicode code to the corresponding text. But string.fromCodePoint () is an improvement over String.fromCharCode().

The method name	Js version	The difference between
formCharCode	es5	Code points greater than 0xFFFF are not recognized and overflow occurs. FromCodePoint is the opposite
formCodePoint	es6	When multiple arguments are passed, they are returned as a string; fromCharCode is not

// Validates 1:0x20bb7 > 0xFFFF
String.fromCharCode(0x20BB7);    / / "ஷ"
String.fromCodePoint(0x20BB7);   / / "𠮷"
String.fromCodePoint(0xFFFF);    / / ""
String.fromCharCode(0xFFFF);    / / ""

// Verify 2: whether multiple arguments are combined into one string
String.fromCodePoint(0x78.0x1f680.0x79) = = ='x\uD83D\uDE80y'     // true
String.fromCharCode(0x78.0x1f680.0x79) = = ='x\uD83D\uDE80y'      // false

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2. String.raw()

Two uses:

One is for template strings, which should not be used with ()
Another is to use (callSite… Substitutions), two parameters: callSite is a template string calling object, should be an object with raw property {raw: [‘foo’, ‘bar’, ‘baz’]}

2.1 String. Raw ` `

Precedes the escape character with a slash

String.raw`Hi\nThe ${2+3}`\ \"Hi\\5"
String.raw`Hi\u000A! `\ \"Hi\\u000A!"
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If the slash of the original string has been escaped (\n)

String.raw`Hi\\n`; \ \"Hi\\\\n"
String.raw`Hi\\n`= ="Hi\\\\n"; \ \true

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2.2 String. Raw (callSite,… substitutions)

Normally, this method is rarely used, but to simulate t${0}e${1}s${2}t

String.raw({raw:'test'},3.4.5)   // "t3e4s5t"

String.raw({raw: ['aa'.'bb'.'cc'].1+2.3})    // "aa3bb3cc"

/ / the following functions and ` aa ${2 + 3} bb ${' Java '+' Script '} cc ` is equal.
String.raw({raw: ['aa'.'bb'.'cc']},2+3.'java'+'Script')  // aa5bbjavaScriptcc
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2.3 String.raw() code implementation

String.raw = function (strings, ... values) {
  let output = ' ';
  let index;
  for (index = 0; index < values.length; index++) {
    output += strings.raw[index] + values[index];
  }

  output += strings.raw[index]
  return output;
}
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3. Example method: codePointAt()

3.1 Instance method, static method, prototype method

First of all, let me tell you what an instance method is. Maybe I’m a chicken, so I don’t know what an instance method is when I hear it. Js method types are: instance method, static method, prototype method three.

Instance methods

Instance methods are defined using the Prototype property of the function object. The object can be used only after it is instantiated

function A (){}
A.prototype.sayHello = function(){
	console.log("Hello")}var a = new A();
a.sayHello();     // Hello
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A static method

It can be called only through the a. method

function A(){}
A.sayHello = function(){
	console.log("Hello")
}
A.sayHello();     //Hello
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Prototype method

Both method instances and constructors in the prototype are accessible

function A(){}
A.prototype.sayHello = function(){
	console.log("Prototype method")
}
A.sayHello = function(){
	console.log("Static method")
}
A.sayHello()     // "static method"
A.prototype.sayHello()     // "prototype method"
let a = new A();
a.sayHello();       // "prototype method"
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A function is an object, and the prototype property in the function object can be thought of as a pointer to a method (so that you don’t have to recreate the method every time you create a new instance with the constructor). This makes sense. Var a is a reference to a, that is, a pointer to sayHello, and a.sayhello () is an error because a is not a pointer, and a.sayhello () is an error because a is not a method object.

CodePointAt () is designed to solve the problem of Unicode code points greater than 0xFFFF not being able to read the entire character

3.2 JavaScript character storage format

Inside javaScript, characters are stored in UTF-16 format.
Each character is fixed to 2 bytes.
For characters that require 4 bytes of storage (characters with a Unicode code point greater than 0xFFFF), javaScript considers them to be two characters.
The code point for the Chinese character “𠮷” (note that this character is not “ji” for “auspicious”) is 0x20BB7, the UTF-16 code is 0xD842 0xDFB7 (55362 57271 in decimal), and requires 4 bytes of storage

var s = "𠮷";
s.length  // 2 The string length is misjudged to be 2
// Returns a two-character decimal point
s.charCodeAt(0) / / 55362
s.charCodeAt(1) / / 57271

// Returns its decimal code point 134071 (i.e., hexadecimal 20BB7)
s.charPointAt(0)  / / 134071
s.charPointAt(1)  / / 57271
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Converts decimal code points to hexadecimal

s.codePointAt(0).toString(16)      // "20bb7"
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3.3 use

The codePointAt() method is the easiest way to test whether a character consists of two bytes or four bytes

function is32Bit(c) {
  return c.codePointAt(0) > 0xFFFF;
}
is32Bit("𠮷") // true
is32Bit("a") // false
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Example method: normalize()

Many European languages have intonation symbols and stress symbols And Unicode provides two methods:

Provide an accented character directly, such as: efforts at decluttering (\u01D1)
Synthesis symbols, for example: O (\u004F) and Welles (\u030C) synthesis (\u004F\u030C)

'\u01D1'= = ='\u004F\u030C' //false
'\u01D1'.length / / 1
'\u004F\u030C'.length / / 2
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The above code javaScript does not recognize that they are the same

4.1 Do not receive parameters

But the normalize() method emmealizes Unicode

'\u01D1'.normalize() === '\u004F\u030C'.normalize()     // true
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4.2 Receiving Parameters

'\u004F\u030C'.normalize('NFC').length / / 1
'\u004F\u030C'.normalize('NFD').length / / 2
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The above code indicates that the NFC parameter returns the synthesized form of the character, and the NFD parameter returns the decomposed form of the character.

However, the Normalize method currently does not recognize compositions of three or more characters. In this case, you can only use regular expressions and use Unicode numbering intervals.

Example methods: includes(), startsWith(), endsWith()

Use: To determine whether a string is contained in another string

JavaScript has an indexOf method

let a ="abcd";
a.indexOf("b");  / / 1
a.indexOf("e");  // -1
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Includes () returns whether the Boolean value contains a character

a.includes("b");    // true
a.includes("f");    // false
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StartsWith (). Returns a Boolean value indicating whether the argument string is at the head of the original string

let a = "abc";
a.startsWith("a");  // true
a.startsWith("b");	// false
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EndsWith (): Returns a Boolean value indicating whether the argument string is at the end of the original string

a.endsWith("c");    // true
a.endsWith("a");    // false
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StartsWith (), endsWith(), and includes() all have a second parameter that indicates the starting position for the search.

let s = 'Hello world! ';
s.startsWith('world'.6) // true
s.endsWith('Hello'.5) // true
s.includes('Hello'.6) // false
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6. Instance method: repeat()

Function: Returns a new string, indicating that the original string is repeated several times

The normal repeat

"x".repeat(3);     // "xxx"
"hello".repeat(2);   // "hellohello"
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"x".repeat(0)    / / ""
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Decimals are rounded down and you’re rounded down

"x".repeat(2.5).  // "xx"
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Negative number or Infinity error

"x".repeat(-1)        // RangeError
"x".repeat(Infinity)  // RangeError
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Negative numbers between 0 and negative 1. They’re all rounded to 0

"x".repeat(-0.3)         / / ""
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NaN is equal to 0

"x".repeat(NaN)         / / ""
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The string is converted to a number first

"x".repeat("2")    // "xx"    
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Example methods: padStart(), padEnd()

7.1 role

Used to complete the string, and padStart() to complete the header. PadEnd () is used for tail completion.

Two parameters:

First: The maximum length for string completion to take effect
Second: the string used for completion

7.2 Passing two parameters

Normal completion

'xxx'.padStart(5."abc");   // "abxxx"
'xxx'.padEnd(5."abc");     // "xxxab"
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If the length of the original string is greater than or = the maximum length (that is, the first parameter), the original string is returned

'xxx'.padStart(2.'ab')     // "xxx"
'xxx'.padEnd(2.'ab')       // "xxx"
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The completion string is truncated if the length of the completion string is greater than the maximum length

'abc'.padStart(10.'0123456789')    // "0123456abc"
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7.3 Omit the second parameter

Omit the second parameter and complete with Spaces by default

'x'.padStart(4) 	// ' x'
'x'.padEnd(4) 		// 'x '
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7.4 use

Specifies bits for numeric completion

'1'.padStart(10.'0')       / / "0000000001"
'123456'.padStart(10.'0') / / "0000123456"
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Prompt string format

'12'.padStart(10.'YYYY-MM-DD')   // "YYYY-MM-12"
'09-12'.padStart(10.'YYYY-MM-DD') // "YYYY-09-12"
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Example methods: trimStart(), trimEnd()

TrimStart () removes whitespace from the string header
TrimEnd () removes whitespace at the end of the string

const s = ' abc ';

s.trim() // "abc"
s.trimStart() // "abc "
s.trimEnd() // " abc"
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The browser also deploytwo additional methods, trimLeft() is an alias for trimStart(), and trimRight() is an alias for trimEnd(). These two uses are the same as trimStart() and trimEnd().

Example method: replaceAll()

9.1 the replace ()

Only the first match can be replaced

'aabbcc'.replace('b'.'_')    // aa_bcc
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To replace all b’s, use the /g modifier

'aabbcc'.replace(/b/g.'_')    // 'aa__cc'
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9.2 replaceAll ()

The first argument passes a string

'aabbcc'.replaceAll('b'.'_')         // "aa__cc"
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The first argument passes the regular expression without the /g modifier replaceAll

/ / is not an error
'aabbcc'.replace(/b/.'_')

/ / an error
'aabbcc'.replaceAll(/b/.'_')
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The second argument is a string that represents the replacement text, where some special strings can be used.

// $& indicates the matching string, which is' b 'itself
// So return the same as the original string
'abbc'.replaceAll('b'.'$&')
// 'abbc'

// $' indicates the string before the match result
// For the first 'b', $' refers to 'a'
// For the second 'b', $' refers to 'ab'
'abbc'.replaceAll('b'.'$`)
// 'aaabc'

// $' indicates the string after the match result
// For the first 'b', $' refers to 'BC'
// For the second 'b', $' refers to 'c'
'abbc'.replaceAll('b'.` $' `)
// 'abccc'

// $1 indicates the first group match of the regular expression and refers to 'ab'
// $2 indicates the second group match of the regular expression, which refers to 'BC'
'abbc'.replaceAll(/(ab)(bc)/g.'$2 $1')
// 'bcab'

// $$refers to $
'abc'.replaceAll('b'.'$$')
// 'a$c'
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The second argument can be a function as well as a string

'aabbcc'.replaceAll('b'.() = > '_')   // 'aa__cc'
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ES6 String addition method

1. String.fromCodePoint()

2. String.raw()

2.1 String. Raw ` `

2.2 String. Raw (callSite,… substitutions)

2.3 String.raw() code implementation

3. Example method: codePointAt()

3.1 Instance method, static method, prototype method

3.2 JavaScript character storage format

3.3 use

Example method: normalize()

4.1 Do not receive parameters

4.2 Receiving Parameters

Example methods: includes(), startsWith(), endsWith()

6. Instance method: repeat()

Example methods: padStart(), padEnd()

7.1 role

7.2 Passing two parameters

7.3 Omit the second parameter

7.4 use

Example methods: trimStart(), trimEnd()

Example method: replaceAll()

9.1 the replace ()

9.2 replaceAll ()

ES6 String addition method

1. String.fromCodePoint()

2. String.raw()

2.1 String. Raw ` `

2.2 String. Raw (callSite,… substitutions)

2.3 String.raw() code implementation

3. Example method: codePointAt()

3.1 Instance method, static method, prototype method

3.2 JavaScript character storage format

3.3 use

Example method: normalize()

4.1 Do not receive parameters

4.2 Receiving Parameters

Example methods: includes(), startsWith(), endsWith()

6. Instance method: repeat()

Example methods: padStart(), padEnd()

7.1 role

7.2 Passing two parameters

7.3 Omit the second parameter

7.4 use

Example methods: trimStart(), trimEnd()

Example method: replaceAll()

9.1 the replace ()

9.2 replaceAll ()

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