A detailed introduction to JavaScript strings-JS Tutorial-php.cn

A detailed introduction to JavaScript strings

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Release： 2017-06-28 13:44:58

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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

&#39;I\&#39;m \"OK\"!&#39;;

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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:

&#39;\x41&#39;; // 完全等同于 &#39;A&#39;

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can also be represented by \u

# represents a Unicode character:

&#39;\u4e2d\u6587&#39;; // 完全等同于 &#39;中文&#39;

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Multi-line string

due to multiple lines It is more troublesome to write strings using \n, so the latest ES6 standard adds a new method of expressing multi-line strings, using `...` to express:

`This is a

Multiple lines

String`;

Template string

To have multiple strings To connect

, you can use the + sign to connect:

var name = &#39;小明&#39;;
var age = 20;
var message = &#39;你好, &#39; + name + &#39;, 你今年&#39; + age + &#39;岁了!&#39;;
alert(message);

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

var name = &#39;小明&#39;;
var age = 20;
var message = `你好, ${name}, 你今年${age}岁了!`;
alert(message);

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Operation string

Common operations on strings are as follows:

var s = &#39;Hello, world!&#39;;
s.length; // 13

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To get the characters at a specified position in the string, use an Array-like The index operation, index

starts from 0:

var s = &#39;Hello, world!&#39;;
s[0]; // &#39;H&#39;
s[6]; // &#39; &#39;
s[7]; // &#39;w&#39;
s[12]; // &#39;!&#39;
s[13]; // undefined 超出范围的索引不会报错，但一律返回undefined

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It should be noted that the string is immutable. There will be no errors in assigning an index, but there will be no effect:

var s = &#39;Test&#39;;
s[0] = &#39;X&#39;;
alert(s); // s仍然为&#39;Test&#39;

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JavaScript provides some common methods for strings. Note that calling these methods itself does not Will change the content of the original string, but return a new string:

toUpperCase

toUpperCase() Change to uppercase:

var s = &#39;Hello&#39;;
s.toUpperCase(); // 返回&#39;HELLO&#39;

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toLowerCase

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

var s = &#39;Hello&#39;;
var lower = s.toLowerCase(); // 返回&#39;hello&#39;并赋值给变量lower
lower; // &#39;hello&#39;

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indexOf

indexOf()会搜索指定字符串出现的位置：
var s = &#39;hello, world&#39;;
s.indexOf(&#39;world&#39;); // 返回7
s.indexOf(&#39;World&#39;); // 没有找到指定的子串，返回-1

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substring

substring()返回指定索引区间的子串：
var s = &#39;hello, world&#39;
s.substring(0, 5); // 从索引0开始到5（不包括5），返回&#39;hello&#39;
s.substring(7); // 从索引7开始到结束，返回&#39;world&#39;

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