JS intercept string (3 methods)

                                                        String Type intercepting string method

Intercepts a string of specified length

substr()  Method can intercept the substring according to the specified length . It has two parameters , The first parameter represents the starting subscript of the substring to be intercepted , The second parameter represents the length of the interception .

Example 1

Use... In the following example  lastIndexOf()  Gets the last position of the subscript in the string , Then intercept from the following position 4  Characters .

var s = "http://c.biancheng.net/index.html";
var b = s.substr(s.lastIndexOf(".") + 1,4);  // After intercepting the last dot 4 Characters 
console.log(b);  // Returns a substring “html”

If you omit the second parameter , It means to intercept all characters from the beginning to the end . Considering that the length of the extension is not fixed , Omitting the second parameter is more flexible . 

var b = s.substr(s.lastIndexOf(".") + 1);

If the first parameter is negative , Indicates that the subscript position is calculated from the end of the string , namely -1 Represents the last character ,-2  Represents the penultimate character , And so on . This is useful when the left character length is not fixed .

ECMAScript  This method is no longer recommended , Recommended  slice()  and  substring()  Method .

Intercept the start and end subscript position string

slice()  and  substring()  Methods intercept the string according to the specified start and end subscript position , They can all contain two parameters , The first parameter represents the starting subscript , The second parameter represents the end subscript .

Example 2

The following code uses  substring()  Method interception URL  Web site host name information in string .

var s  = "http://c.biancheng.net/index.html";
var a = s.indexOf("c");
var b = s.indexOf("/", a);
var c = s.substring(a,b);
var d = s.slice(a,b);

• The intercepted string contains the character specified by the first parameter . The end point is not intercepted , That is, it is not included in the string .
• If the second parameter is omitted , Represents all strings intercepted to the end .

If the value of the first parameter is greater than the value of the second parameter ,substring()  Method can exchange two parameters before performing interception , And for  slice()  methods , Is ignored as invalid , And return an empty string .

Example 3

The following code compares  substring()  Methods and  slice()  Different methods and usages .

var s = "http://c.biancheng.net/index.html";
var a = s.indexOf("c");
var b = s.indexOf("/", a);
var c = s.substring(b, a);
var d = s.slice(b, a);

• When the values of the start and end points cannot be determined , Use  substring()  More appropriate .
• If the parameter value is negative ,slice()  Method can interpret the minus sign as positioning from the right , This is related to Array  Of slice()  In the same way . however  substring()  Method will treat it as invalid , And return an empty string .

Example 4

The following code compares  substring()  Methods and  slice()  Methods are used differently .

var s = "http://c.biancheng.net/index.html";
var a = s.indexOf("c");
var b = s.indexOf("/", a);
var 1 = s.length;
var c = s.substring(a-1, b-1);
var d = s.slice(a-1, b-1);