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directory

  1. CRUD
  2. increase
  3. delete
  4. change
  5. checkstr[1] indexOf, etc.Return element position | | Boolean value

A CRUD add delete change check

Read from the definition of CRUD, which is an acronym for the words increase (Create), read (Retrieve), Update (Update) and Delete (Delete) when performing computations

2 to add

Create string: Literal string object style

var str = 'abc'; // 'abc'
var str1 = new String('a'); // String {'a'}
str1.toString(); // 'a'
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Three delete

1) Remove the STR whitespacetrim() trimStart() trimEnd()

Trim () trimStart() trimEnd() These three methods can be used to remove whitespace characters at the beginning and end of a string. Whitespace characters include Spaces, tabs, and newlines

var str = ' a b '
str.trim(); // 'a b'
str.trimStart(); // 'a b '
str.trimEnd(); //' a b'

str.trimLeft(); // 'a b '
str.trimRight(); // ' a b'
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Four change

1) String concatenation + concat

var str = 'abc';
var str1 = str+'00'; // 'abc00'
str.concat('d'.'e'); // 'abcde'
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2) split STR = > array

var str = 'a,b; c.d';
str.split(/[,;.]/);
// ['a', 'b', 'c', 'd']

var str = 'abcd';
str.split(' '); // ['a', 'b', 'c', 'd']
var str = 'abcd';
str.split(); // ['abcd']
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3) toLowerCase toUpperCase

var str = 'AbCd';
str.toLowerCase(); // 'abcd'
var str = 'AbCd';
str.toUpperCase(); // 'ABCD'
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4) Intercept stringssubstr substring slice

Substr Slice subString can be used to intercept strings without changing the original data. The second argument is optional. The first two arguments can be passed negative numbers

4.1) slice Positive sequence rules Do not change the raw data Both parameters can be negative

Used to extract a portion of a string and return the extracted portion as a new string

string.slice(start,end)
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var str = 'abc';
var str1 = str.slice(1);
console.log(str,str1);
// 'abc' 'bc'
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var str = 'abc';
var str1 = str.slice(-2, -1);
console.log(str,str1); // abc b
var str1 = str.slice(-2);
console.log(str,str1); // abc bc
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The substring returned by this method includes the character at the beginning, but not the character at the end

4.2) substr

The substr method is used to extract a specified number of characters from the beginning subscript in a string. The syntax is as follows: start is a negative number. -1 is the last character in the string, -2 is the penultimate character, and so on.

string.substr(start,length)
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var str = 'abc';
var str1 = str.substr(-1);
console.log(str,str1);
// abc c
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4.3) substring Both parameters must be positive

The substring() method is used to extract the character of a string intermediate between two specified subscripts

string.substring(from, to)
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var str = "abcdefg";
str.substring(1.5); //'bcde'
var str1 = str.substring(1); // 'bcdefg'
console.log(str,str1); // "abcdefg" 'bcdefg'
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5) The string is converted to a numberparseInt() 和 parseFloat()

The parseInt() and parseFloat() methods are both used to convert strings to numbers.

parseFloat("10.001")  / / 10.001
parseInt("10.001") / / 10
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6) is lackingpadStart padEnd

'p'.padStart(5.'ab') // 'ababp'

'a'.padStart(5) // 'a' does not pass the second argument, default is space

'a'.padEnd(5.'i'); // 'aiiii'
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7) repeatrepeat

'na'.repeat(0) / /"
'a'.repeat(3) // 'aaa'
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Five checkstr[1] indexOf, etc.Return element position | | Boolean value

1) Get the stringSpecifies the value of the location charAt()andcharCodeAt()

Both the charAt() and charCodeAt() methods can be indexed to get a value at a given location:

  • The charAt() method getsThe character that specifies the position;
  • The charCodeAt() method gets the positional characterUnicode value

CharCodeAt () returns an integer between 0 and 65535, or NaN if there are no characters at the specified position

CharCodeAt passes numbers and strings the same way.

str.charCodeAt(0); / / 97
'0'.charCodeAt('0'); / / 48
'0'.charCodeAt(0); / / 48
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2) charAt() 与 str[1]The difference between

STR [index] returns undefined and charAt(index) returns an empty string when index is not in the length range of STR.

var str = 'abc';
str[1]; // 'b'
str[3]; // undefined
str.charAt(3); / /"
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3) Retrieve the stringWhether a particular sequence is included indexOf lastIndexOf includes startsWith endsWith

Note: All 5 methods are case-sensitive

3.1) indexOf lastIndexOf The position of the return value
  • IndexOf [to find in positive order]: Looks for a character,With the returnThe position that was first matchedOtherwise, -1 is returned
  • LastIndexOf [reverse lookup]: Searches for a character, if any, returnsThe location of the last matchOtherwise, -1 is returned
var str = 'abcabc';
str.indexOf('a'); / / 0
str.indexOf('a'.3); / / 3
str.indexOf('a'.4); // -1

var str = 'abcabc';
str.indexOf('bc'); / / 1
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3.2) includes startsWith endsWith Return to Boerse
  • includes(): This method is used to judge stringsWhether to contain the specified substring
  • startsWith(): This method is used to detect stringsWhether to start with the specified substring
  • endsWith: This method is used to determine the current stringEnds in the specified substring
var str = 'abcabc';
str.includes('abcd');
str.includes('ab');
str.includes('ab'.5);
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var str = 'abcabc';

str.startsWith('b'); // false
str.startsWith('abc'); // true

str.endsWith('bc'); // true
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4) Get the STR itselfvalueOf() 和 toString()

Both the valueOf() and toString() methods return the valueOf the string itself

var str = 'abc';
str.toString(); // 'abc'
str.valueOf(); // 'abc'

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5) STR pattern matching replace() match() search()

The replace replaceAll match search method can be used to match or replace characters

var str = 'abcbc';
str.replace('bc'.1); // 'a1bc'
var str = 'abcbc';
str.replaceAll('bc'.1);//'a11'
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var str = 'aBCabc';
var str1 = str.replace(/ab/gi.1);
console.log(str,str1);
// 'aBCabc' '1C1c'
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var str = 'aBCabc';
str.match('ab');
// ['ab', index: 3, input: 'aBCabc', groups: undefined]
var str = 'aBCabc';
str.match('d'); // null
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var str = "abcdef";
str.search(/bcd/); / / 1
var str = "abcdef";
str.search('c'); / / 2
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reference

  • JS top 20 common string methods and their usage
  • Js 28 common string methods and use tips

conclusion

  • IndexOf [to find in positive order] LastIndexOf [reverse lookup]
  • substr slice substringCan be used to intercept strings,They don't change the raw data The second parameter is optional The first two first arguments can both be passed negative numbers
  • slice Positive sequence rules Do not change the raw data Both parameters can be negative