A detailed introduction to JavaScript strings

String in JavaScript is represented by characters enclosed in '' or "". The following article will introduce you to the relevant knowledge of JavaScript strings. Friends who are interested should take a look.

JavaScript strings are 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: the string represented by

'I\'m \"OK\"!';

The content is: I'm "OK"!

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

ASCII characters can be represented in hexadecimal format in the form of \x##, for example:

'\x41'; // 完全等同于 'A'

can also be represented by \u

'\u4e2d\u6587'; // 完全等同于 '中文'

Template string

To have multiple strings To connect

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

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

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

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

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

toUpperCase

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

##toLowerCase() changes a string to all lowercase :

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

indexOf

##

indexOf()会搜索指定字符串出现的位置：
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()返回指定索引区间的子串：
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'

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