What are the javascript strings?

What are JavaScript strings?

As one of the main languages ​​​​for web front-end development, JavaScript is very flexible in processing various data types, and strings are one of them. This article will introduce the basic concepts, usage and common methods of JavaScript strings.

What is a JavaScript string?

In JavaScript, a string is a sequence of 0 or more characters. A string can contain letters, numbers, punctuation marks, and special characters such as spaces, tabs, and newlines. Its length can be determined based on the number of characters in it. Strings can be defined and represented using single quotes, double quotes, or backslashes.

Here are some examples:

//Use single quotes to define strings
var str1 = 'Hello World!';

//Use double quotes to define characters String
var str2 = "Hello World!";

//Use backslashes to define strings
var str3 = "Hello
World!";

/ /Multi-line string
var str4 = `This is a
multi-line
string!`;

Usage of JavaScript string

JavaScript string can be used In various situations, such as outputting text, splicing other types of data, etc. Here are some examples of using strings:

//Output string
console.log("Hello World!");

//Splicing string
var str1 = "Hello";
var str2 = "World";
var result = str1 " " str2;
console.log(result); //Output "Hello World"

/ /Convert other types of data to string type
var num = 123;
var str = num.toString(); //Convert numeric type to string type

JavaScript string Common methods

JavaScript strings There are many common methods that can be used to easily operate on strings, some of which are introduced below.

1. length method

The length method is used to get the length of a string, that is, the number of characters contained in it.

var str = "Hello World!";
console.log(str.length); //Output 12

2. toUpperCase and toLowerCase methods

The toUpperCase method converts all lowercase letters in the string to uppercase letters, while the toLowerCase method converts all uppercase letters in the string to lowercase letters.

var str = "Hello World!";
console.log(str.toUpperCase()); //Output HELLO WORLD!
console.log(str.toLowerCase()); / /Output hello world!

3. indexOf and lastIndexOf methods

The indexOf method is used to find the first occurrence of a specified character or substring in a string, and the lastIndexOf method It is to find the last occurrence position.

var str = "Hello World!";
console.log(str.indexOf("o")); //Output 4
console.log(str.lastIndexOf("o" )); //Output 7

4. slice and substring methods

The slice method and substring method are both used to intercept a specified substring in the string.

The parameter of the slice method can be a positive number or a negative number, where a positive number means counting from the beginning of the string, and a negative number means counting from the end of the string. If the second parameter is omitted, it means that the position of the first parameter is intercepted to the end of the string.

var str = "Hello World!";
console.log(str.slice(1, 5)); //Output "ello"
console.log(str.slice(-- 6)); //Output "World!"

The parameters of the substring method can also be positive or negative, but negative numbers cannot be used as parameters. If the second parameter is omitted, it means that the parameter is from the first parameter. The position is truncated to the end of the string.

var str = "Hello World!";
console.log(str.substring(1, 5)); //Output "ello"
console.log(str.substring(6 )); //Output "World!"

5. replace method

Thereplace method is used to replace the specified character or substring in the string with a new character or substring.

var str = "Hello World!";
console.log(str.replace("World", "JavaScript")); //Output "Hello JavaScript!"

Summary

JavaScript string is a sequence of 0 or more characters whose length can be determined based on the number of characters in it. Strings can be defined and represented using single quotes, double quotes, or backslashes. JavaScript strings can be used in various situations, such as outputting text, splicing other types of data, etc. There are many commonly used methods in JavaScript that can easily operate on strings, such as length, toUpperCase, toLowerCase, indexOf, lastIndexOf, slice, substring, and replace.

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