JavaScript string

JavaScript string

JavaScript string is represented by characters enclosed in '' or "".

If ' itself is also a character, it can be enclosed by "". For example, "I'm OK" contains the six characters I, ', m, space, O, and K.

What if the string contains both ' and "? It can be identified by the escape character \, for example:

'I\'m \"OK\"!';

means the content of the string is: I'm "OK" !

The escape character \ can escape many characters, such as \n representing a newline, \t representing a tab character, and the character \ itself must be escaped, so the character represented by \\ is \.

'\x41'; // 完全等同于 'A'

# to represent a Unicode character:

'\u4e2d\u6587'; // 完全等同于 '中文'

Multi-line string

Since multi-line strings are more troublesome to write using \n, the latest ES6 standard adds a new method of expressing multi-line strings, using `... ` means:

`这是一个
多行
字符串`;

Exercise: Test whether your browser supports the ES6 standard. If it does not support it, please re-express the multi-line string with \n:

// If the browser ES6 is not supported and a SyntaxError will be reported:

alert(`多行
字符串
测试`);

Template string

To connect multiple strings, you can use the + sign to connect:

var name = '小明';
var age = 20;
var message = '你好, ' + name + ', 你今年' + age + '岁了!';
alert(message);

If there are many variables that need to be connected, it is more troublesome to use the + sign. ES6 has a new template string, which is expressed in the same way as the above multi-line string, but it will automatically replace the string in the string. Variable:

var name = '小明';
var age = 20;
var message = `你好, ${name}, 你今年${age}岁了!`;
alert(message);

Exercise: Test whether your browser supports ES6 template strings. If not, please change the template string to a + connected ordinary string:

// If The browser supports template strings and will replace variables inside the string:

var name = '小明';
var age = 20;
alert(`你好, ${name}, 你今年${age}岁了!`);

Operation string

Common operations on strings are as follows:

var s = 'Hello, world!';
s.length; // 13

To get the characters at a specified position in the string, use an Array-like subscript operation. The index number starts from 0:

var s = 'Hello, world!';
s[0]; // 'H'
s[6]; // ' '
s[7]; // 'w'
s[12]; // '!'
s[13]; // undefined 超出范围的索引不会报错，但一律返回undefined

It is important to note that the string is immutable. If you assign a value to an index of the string, there will be no errors, but there will be no effect:

var s = 'Test';
s[0] = 'X';
alert(s); // s仍然为'Test'

JavaScript provides some common methods for strings. Note that calling these methods will not change the original has the content of a string, but returns a new string:

toUpperCase

toUpperCase() changes a string to all uppercase:

var s = 'Hello';
s.toUpperCase(); // 返回'HELLO'

toLowerCase

var s = 'Hello';
var lower = s.toLowerCase(); // 返回'hello'并赋值给变量lower
lower; // 'hello'

indexOf

indexOf() will search for the location where the specified string appears:

var s = 'hello, world';
s.indexOf('world'); // 返回7
s.indexOf('World'); // 没有找到指定的子串，返回-1

substring

substring()Returns the substring of the specified index interval:

'var s = 'hello, world'
s.substring(0, 5); // 从索引0开始到5（不包括5），返回'hello'
s.substring(7); // 从索引7开始到结束，返回'world'