JS string learning how to return the substring between given subscripts

In the previous article "JS String Learning: Calculate all occurrence positions of a given character", we introduced the use of indexOf() and lastIndexOf() functions combined with a while loop to obtain the given substring Method to string all positions in a string. So today I will continue to bring you the JavaScript string learning series~

This article will introduce to you two methods of intercepting strings with JavaScript and obtaining all characters (i.e. substrings) between specified positions.

First let's take a look at the first method - using slice()

As an example~

var str="Hello world!"; 
var n=str.slice(1,7);
console.log("原字符串："+str);
console.log("截取下标1~7之间的子串："+n);

Let's take a look at the output results :

Because the string subscript starts from 0, use str.slice(1,7) to intercept subscript 1 Characters between ~7, the returned substring is "ello w".

Let’s take a look at the slice() function

string.slice(start,end)The method can extract a certain part of the string and use it as a new The string returns the extracted part; this function accepts a required parameter start and an omitted parameter end.

• start parameter: indicates the starting subscript; the first character position is 0. If it is a negative number, it is intercepted from the end.

• end parameter: indicates the end subscript. If this parameter is not specified, the split array contains all elements from start to the end of the array; if this parameter is a negative number, it specifies the elements starting from the end of the array.

var str="Hello world!"; 
var n=str.slice(1,-7);
console.log("原字符串："+str);
console.log("截取到的子串："+n);

Output result:

Next let’s take a look at the second method - using substring() Method

For example~

var str="Hello world!"; 
var n=str.substring(1,7);
console.log("原字符串："+str);
console.log("截取到的子串："+n);

Output result:

The substring() method can extract the string between two characters between specified subscripts. We use str.substring(1,7) to intercept the characters between the string str subscript 1~7, so the returned substring is "ello w".

Let’s take a look at the substring() function.

string.substring(from, to)The method accepts a required parameter from (a non-negative integer, specifying the starting subscript), and an omitted parameter to (specifying the ending subscript) ). The substring returned by the substring() method includes the characters at the beginning but does not include the characters at the end.

The difference between slice() and substring():

Both slice() and substring() can intercept strings according to the specified starting and ending subscript positions. It can contain two parameters, the first parameter represents the starting subscript, and the second parameter represents the ending subscript.

But if the first parameter value is greater than the second parameter value, the substring() method can exchange the two parameters before performing interception, but for the slice() method, it is ignored and considered invalid. , and returns an empty string.

var str="Hello world!"; 
var n1=str.substring(7,1);
var n2=str.slice(7,1);
console.log("原字符串："+str);
console.log("截取到的子串："+n1);
console.log("截取到的子串："+n2);

Output result:

If the parameter value is a negative value, the slice() method can interpret the negative sign as positioning from the right; and substring () method will treat it as invalid.

var str="Hello world!"; 
var n1=str.substring(1,-7);
var n2=str.slice(1,-7);
console.log("原字符串："+str);
console.log("截取到的子串："+n1);
console.log("截取到的子串："+n2);

Output result:

Okay, that’s all. If you need it, you can read: javascript advanced tutorial

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