JS string interception method summary

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One 、 Use slice() Intercept

1, Function description

slice() Method by specifying the start and end positions , Extract a part of the string , And return the extracted part with a new string .

The grammar is as follows ：

string.slice(start, end); start（ It's necessary ）： Specify where to start selecting . If it's a negative number , Then it specifies the position from the end of the string . in other words ,-1 Refers to the last character ,-2 Refers to the penultimate character , And so on . Parameter description ：

end（ Optional ）： Specify where to end the selection , That is, the character subscript at the end . If the parameter is not specified , Then the intercepted string contains from start All characters to the end . If this parameter is negative , Then it specifies the characters starting from the end of the array .

2, Use samples

var str = “0123456789”;

console.log(“ Original string ：”, str);

console.log(“ From index to 3 From character to end ：”, str.slice(3)); //3456789

console.log(“ From the bottom of the first 3 From character to character ：”, str.slice(-3)); //789

console.log(“ From the beginning until the index is 5 The previous character of ：”, str.slice(0,5)); //01234

console.log(“ From the beginning to the penultimate 3 The first character of a character ：”, str.slice(0,-3)); //0123456

console.log(“ From index to 3 The character of is indexed as 5 The previous character of ：”, str.slice(3,5)); //34

console.log(“ From index to 3 The character of starts from the penultimate 3 The first character of a character ：”, str.slice(3,-3)); //3456

Two 、 Use substring() Intercept

1, Function description

（1）substring Method is used to extract characters that are mediated between two specified subscripts .

The grammar is as follows ：

string.substring(start, stop)

start（ It's necessary ）： A nonnegative integer , Specifies that the first character of the substring to be extracted is in stringObject Position in . Parameter description ：

stop（ Optional ）： A nonnegative integer , The last character of the substring to be extracted is in stringObject There are many places in 1.

Return value description ： This method returns a new string , The string value contains stringObject A substring of , Its content is from start Go to stop-1 All characters at , The length of stop reduce start.

（2） matters needing attention ：

• If start And end equal , Then the method returns an empty string （ The length is 0 String ）.
• If start Than end Big , Then the method will exchange these two parameters before extracting the substring .
• If start or end It's a negative number , It will be replaced by 0.

2, Use samples

var str = “0123456789”;

console.log(“ Original string ：”, str);

console.log(“ From index to 3 From character to end ：”, str.substring(3)); //3456789

console.log(“ From index to 20 From character to end ：”, str.substring(20)); //

console.log(“ From index to 3 The character of is indexed as 5 The previous character of the ends ：”, str.substring(3,5)); //34

console.log(“start Than end Conference automatic exchange , The same as above ：”, str.substring(5,3)); //34

console.log(“ From index to 3 The character of is indexed as 20 The previous character of the ends ：”, str.substring(3,20)); //3456789

3、 ... and 、 Use substr() Intercept

1, Function description

substr Method is used to return a substring of a specified length starting at a specified position .

The grammar is as follows ：

stringObject.substr(start, length); start（ It's necessary ）： The starting position of the required substring . The index of the first character in the string is 0. length（ Optional ）： The number of characters that should be included in the returned substring .

（2） matters needing attention ：

• If length by 0 Or negative numbers , Will return an empty string .
• If not specified length, Then the substring will continue to stringObject Last .
• If start or length It's a negative number , It will be replaced by 0.

2, Use samples

var str = “0123456789”;

console.log(“ Original string ：”, str);

console.log(“ From index to 3 From character to end ：”, str.substr(3)); //3456789

console.log(“ From index to 20 From character to end ：”, str.substr(20)); //

console.log(“ From index to 3 The intercept length from the character of is 5 String ：”, str.substr(3,5)); //34567

console.log(“ From index to 3 The intercept length from the character of is 20 String ：”, str.substr(3,20)); //3456789

Four 、 Other common methods

1,indexOf()

Returns the subscript of the first character in a string that matches a substring .

var str = “JavaScript”;

var i1 = str.indexOf(“a”); //1

var i2 = str.indexOf(“S”); //4

var i3 = str.indexOf(“Script”); //4

var i4 = str.indexOf(“k”); //-1

console.log(“ Original string ：”, str);

console.log(“a The index of ：”, i1);

console.log(“S The index of ：”,i2);

console.log(“Script The index of ：”,i3);

console.log(“k The index of ：”,i4);

2,lastIndexOf()

This method returns the index value of the first character of a character or string from right to left （ And indexOf contrary ）

var str = “JavaScript”;

var i1 = str.lastIndexOf(“a”); //3

var i2 = str.lastIndexOf(“S”); //4

var i3 = str.lastIndexOf(“Script”); //4

var i4 = str.lastIndexOf(“k”); //-1

3,split()

Use a specified separator to partition a string into an array .

var str = “jpg|bmp|gif|ico|png”;

var arr= str.split(“|”);

console.log(arr);

4,join()

Combines an array into a string using a specified delimiter .

var arr= new Array(“jpg”,”bmp”,”gif”,”ico”,”png”);

var str = arr.join(“|”);

console.log(str);

5,concat()

Join two arrays together .

var arr1 = [1, 2, 3];

var arr2 = [4, 5, 6];

var arr3 = arr1.concat(arr2);

console.log(arr3);

6,charAt()

Returns the character in the specified position . The subscript of the first character in the string is 0. If parameters index be not in 0 And string.length Between , This method will return an empty string .

var str = “abcdefg”;

var char = str.charAt(2); //c

console.log(char);

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