Summary of JS common string API in javaScript tutorial

1. String and array have some similarities. They can get the size through length attribute, can be accessed through subscript, and can traverse each character / element with for loop
2. The difference between strings and arrays is that arrays can be modified at will. Strings are read-only arrays of characters. Once created, they cannot be modified

1. String splicing concat(), +, template string

concat() function: concatenate multiple strings into a new string and return the new concatenated string
Syntax: VAR newstr= str.concat (string1,string2,… ,stringx)

var str = "dream-"; var str1 = "starts"; var str2 = "-with-lighting-matches"; var newStr1 = str.concat();//No parameter function equivalent to copy string var newStr2 = str.concat(str1);//Splicing str and str1 back var newStr3 = str.concat(str1,str2); //Splicing str with str1 and str2 console.log(newStr1)//dream- console.log(newStr2);//dream-starts console.log(newStr3);//dream-starts-with-lighting-matches

Concatenate strings with
Usage: var newStr = str + string1 + string2 + +stringx

var str = "dream-"; var str1 = "starts"; var str2 = "-with-lighting-matches"; var newStr1 = str + str1;//Splicing str with str1 var newStr2 = str + str1 + str2; //Splicing str with str1 and str2 console.log(newStr1);//dream-starts console.log(newStr2);//dream-starts-with-lighting-matches

Splicing string ES6 through template string NEW
Usage: var newStr = $$...$

//Usage: var newStr = `$$...$` var str = "dream"; var str1 = "starts"; var str2 = "with-lighting-matches"; var newStr1 = `${str}-${str1}`;//Splicing str with str1 var newStr2 = `${str}-${str1}-${str2}`; //Splicing str with str1 and str2 console.log(newStr1);//dream-starts console.log(newStr2);//dream-starts-with-lighting-matches

2. Select substring(), substr(), slice()

substring() function: select a string between two specified indexes. The two parameters follow the principle of including the head but not the tail, and return the newly selected string
Syntax: VAR newstr= str.substring ([starti [,endi]])
Note: substring will start with a smaller parameter and end with a larger parameter

var str = "dream-starts-with-lighting-matches"; var newStr1 = str.substring();//No parameter to select all characters var newStr2 = str.substring(5);//A parameter represents the start position. Select the start to end character from index 5 var newStr3 = str.substring(5,10); //Select the characters between index 5 and index 10, excluding index 10 //Take the smaller parameter as the starting position and the larger parameter as the ending position var newStr4 = str.substring(10,5); //Select the characters between index 5 and index 10, excluding index 10 console.log(newStr1)//dream-starts-with-lighting-matches console.log(newStr2);//-starts-with-lighting-matches console.log(newStr3);//-star console.log(newStr4);//-star

substr() function: selects a string of a specified length from a specified location, and returns the newly selected string
Syntax: VAR newstr= str.substr ([starti [,length]])

var str = "dream-starts-with-lighting-matches"; var newStr1 = str.substr();//No parameter to select all characters var newStr2 = str.substr(5);//A parameter represents the start position. Select the character from index position 5 to the end var newStr3 = str.substr(5,8);//Select 8 characters from index position 5 console.log(newStr1)//dream-starts-with-lighting-matches console.log(newStr2);//-starts-with-lighting-matches console.log(newStr3);//-starts-

slice() function: select the string between two specified indexes. The two parameters follow the principle of including the head and not the tail, and return the newly selected string
Syntax: VAR newstr= str.slice ([starti [,endi]])

var str = "dream-starts-with-lighting-matches"; var newStr1 = str.slice();//No parameter to select all characters var newStr2 = str.slice(5);//A parameter represents the start position. Select the start to end character from index 5 var newStr3 = str.slice(5,10); //Select the characters between index 5 and index 10, excluding index 10 console.log(newStr1)//dream-starts-with-lighting-matches console.log(newStr2);//-starts-with-lighting-matches console.log(newStr3);//-star

3. String search indexOf(), lastIndexOf(), search(), match(), exec()

indexOf() function: search the specified value from the beginning to the end, return the first index of the specified value, and return - 1 if not found
Syntax: VAR index= str.indexOf (searchvalue [,fromindex])

var str = "Good good good study, day day day up"; var index1 = str.indexOf('good'); console.log(index1);//5 var index2 = str.indexOf('good',6); console.log(index2);//10 var index3 = str.indexOf('No'); console.log(index3);//-1

lastIndexOf() function: search for the specified value from the end of the string, return the first index of the specified value, and return - 1 if not found
Syntax: VAR index= str.lastIndexOf (searchvalue [,fromindex])

var str = "Good good good study, day day day up"; var index1 = str.lastIndexOf('good'); console.log(index1);//10 var index2 = str.lastIndexOf('good',6); console.log(index2);//5 var index3 = str.lastIndexOf('good',3); console.log(index3);//-1

search() function: find the position of the specified value / regular matching value in the string, return the first index found, and return - 1 if not found
Syntax: VAR index= str.search (regexp/searchvalue )

var str = "Good good good study, Day day day up"; var index1 = str.search('good'); console.log(index1);//5 var index2 = str.search('No'); console.log(index2);//-1 var index3 = str.search(/good/); console.log(index3);//5 var index3 = str.search(/good/i);//Case insensitive based on regular lookup console.log(index3);//0

match() function: find the element of the specified value / regular match. The return value is different according to whether the global match (whether there is a g identifier in the regular). null is not found, as follows:

1. The parameter is non regular or regular but does not match globally. An array is returned. The array members are as follows:
   Element 0: match text
   index: the location of the first match to the substring
   input: original string
   groups: not currently supported

2. Parameter is regular global match: returns an array of all matched values

Syntax: var arr= str.match(regexp/searchvalue )

var str = "Good good good study"; var arr1 = str.match('good'); console.log(arr1);//["good", index: 5, input: "Good good good study", groups: undefined] var arr2= str.match('No'); console.log(arr2);//null var arr3= str.match(/good/); console.log(arr3);//["good", index: 5, input: "Good good good study", groups: undefined] var arr4 = str.match(/good/g);//Global lookup, case sensitive console.log(arr4);//["good", "good"] var arr5 = str.match(/good/ig);//Global lookup, case insensitive console.log(arr5);// ["Good", "good", "good"] var arr6 = str.match(/No/ig);//Global lookup, case insensitive console.log(arr6);// null

exec() function: find the regular matching element, return null if not found, and return the new array. The array members are as follows:

• Element 0: match text
• index: the location of the first match to the substring
• input: original string
• groups: not currently supported

The value of the lastIndex attribute in different regular objects in the call process of global matching (whether there is a g identifier) is used to control the start position of the check character. If it is a non global matching, the value is zero. If it is a global matching, the value is the next bit of the tail index of the last string found

Syntax: VAR arr= regexp.exec (str)

Appendix: two ways of regular definition

1. var regexp = /pattern/modifiers;
2. var regexp = new RegExp(pattern,modifiers);

• Modifiers Description:
  i: Ignore case;
  g: Global matching;
  m: Multi line matching, when the string to be retrieved is a single line, it is meaningless to use M

var str = "Good good good study"; var regexp1 = /good/ var arr1 = regexp1.exec(str); console.log(arr1);//["good", index: 5, input: "Good good good study", groups: undefined] //var regexp2 = /good/g var regexp2 = new RegExp(/good/,"g") do { console.log(arr2) console.log(regexp2.lastIndex) } while ((arr2 = regexp2 .exec(str)) != null) //Do while will loop output three times, each time as follows //for the first time //null //0 //The second time //["good", index: 5, input: "Good good good study", groups: undefined] //9 //third time //["good", index: 10, input: "Good good good study", groups: undefined] //14

4. Replace string ()

replace() function: replace the matching content in the string with the new content, and return the replaced string
Syntax: VAR newstr= str.replace (regexp/substr,replacement)

var str = "Good good good study, day day day up"; var newStr1 = str.replace('good','hard');//Normal replace only replaces the first matching position var newStr2 = str.replace(/good/g,'hard');//Use regular global find replace, case sensitive var newStr3 = str.replace(/good/ig,'hard');//Use regular global lookup to replace, case insensitive var newStr4 = str.replace(/\s+/g,'');//Remove space console.log(newStr1)//Good hard good study, day day day up console.log(newStr2);//Good hard hard study, day day day up console.log(newStr3);//hard hard hard study, day day day up console.log(newStr4);//Goodgoodgoodstudy,daydaydayup

5. Split string into array split()

split() function: splits a string into arrays according to the specified separator, and returns the array generated by the split string
Syntax: VAR newarr= str.split (separator,howmany)

var str1 = "dream-starts-with-lighting-matches"; var newArr1 = str1.split('-');//Split string into arrays based on '-' var newArr2 = str1.split('-', 3);//Split the string into arrays according to '-', only the first three console.log(newArr1)//["dream", "starts", "with", "lighting", "matches"] console.log(newArr2);//["dream", "starts", "with"] //Expand. split is usually used with join var str1 = "dream-starts-with-lighting-matches"; var newArr3 = str1.split('-');//Split string into arrays based on '-' var str3 = newArr3.join('&') console.log(newArr1)//["dream", "starts", "with", "lighting", "matches"] console.log(str3)//dream&starts&with&lighting&matches

6. String case conversion to lowercase(), to uppercase()

toLowerCase() function: converts all characters in a string to lowercase, and returns the converted String
Syntax: VAR newstr= str.toLowerCase ()
toUpperCase() function: converts all characters in a string to uppercase, and returns the converted String
Syntax: VAR newstr= str.toUpperCase ()

var str = "Good good study, Day day up"; var newStr1 = str.toLowerCase(); var newStr2 = str.toUpperCase(); console.log(newStr1)//good good study, day day up console.log(newStr2);//GOOD GOOD STUDY, DAY DAY UP

7. Get charAt() and charCodeAt() of the specified position

charAt() function: gets the character of the specified position / index in the string, and returns the obtained character
Syntax: VAR newchar= str.charAt (index)

charCodeAt() function: gets the character code of the specified position / index in the string, and returns the obtained character code
Syntax: VAR newcharcode= str.charCodeAt (index)

var str = "Good good study, Day day up"; var char1 = str.charAt(0); var char2 = str.charAt(5); var charCode1 = str.charCodeAt(0); var charCode2 = str.charCodeAt(5); console.log(char1)//G console.log(char2);//g console.log(charCode1);//ASCII code of 71 character G console.log(charCode2);//ASCII code of 103 character g