How to define string in javascript

Method: 1. Use double quotes or single quotes to include text of any length, such as ""true""; 2. Use the String() type function to construct a string, the syntax is "new String("value") "; 3. Use the fromCharCode() method to convert the character encoding into a string.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

In JavaScript, there are the following 3 ways to define strings.

String literals

Use double or single quotes to enclose text of any length.

Example 1

Any text enclosed in quotation marks is called string data.

var s = "true";  //把布尔值转换为字符串
var s = "123";  //把数值转换为字符串
var s = "[1,2,3]";  //把数组转换为字符串
var s = "{x : 1; y : 2}";  //把对象转换为字符串
var s = "console.log('Hello,World')";  //把可执行表达式转换为字符串

Example 2

Single quotes and double quotes can be used together to define special forms of strings.

var s = 'console.log("Hello,World")';

Single quotes can contain double quotes, or double quotes contain single quotes. However, you cannot include single quotes within single quotes, or double quotes within double quotes.

Example 3

Because some characters contain multiple semantics, they need to be escaped in the string to avoid ambiguity. The basic way to escape characters: add a backslash before the character.

var s = "\"";  //有效的引号字符

Example 4

For stringified scripts, you can call the global method eval() to execute the string code.

var s = "console.log('Hello,World')";  //表达式字符串
eval(s);  //执行表达式字符串

Constructing a string

Using the String() type function to construct a string, the function can receive a parameter and use it as value to initialize the string.

Example 5

The following uses the new operator to call the String() constructor to create a string object.

var s = new String();  //创建一个空字符串对象，并赋值给变量s
var s = new String("我是构造字符串");  //创建字符串对象，初始化之后赋值给变量s

Through the String constructor, the type of the constructed string is different from that of the string literal. The former is a reference object, and the latter is a value type string

Example 6

The following code compares the differences in the data types of constructed strings and string literals.

var s1 = new String(1);  //构造字符串
var s2 = "1";  //定义字符串直接量
console.log(typeof s1);  //返回object，说明是引用型对象
console.log(typeof s2);  //返回string，说明是值类型字符串

Example 7

String() can also be used as a normal function to convert the parameters into a string type value and return it.

var s = String(123456);  //包装字符串
console.log(s);  //返回字符串“123465”
console.log(typeof s);  //返回string，说明是简单的值

Example 8

String() allows multiple parameters to be passed in, but only processes the first parameter and converts it into a string and returns it.

var s = String(1,2,3,4,5,6);  //带有多个参数
console.log(s);  //返回字符串“1”
console.log(typeof s);  //返回string，数值被转换为字符串

However, all parameter expressions will be evaluated by JavaScript.

Example 9

After the following variable n is calculated multiple times in the constructor, the final value is incremented to 5.

var n = 1;  //初始化变量
var s = new String(++n; ++n; ++n; ++n);  //字符串构造处理
console.log(s);  //返回2
console.log(n);  //返回5
console.log(typeof s);  //返回object，说明是引用型对象
console.log(typeof n);  //返回number，说明是数值类型

Use character encoding

Use the fromCharCode() method to convert the character encoding into a string. This method can contain multiple integer parameters, each parameter represents the Unicode encoding of the character, and the return value is a string representation of the character encoding.

Example 10

The following code demonstrates how to convert a set of string encodings into a string.

var a = [35835,32773,24744,22909], b = [];  //声明一个字符编码的数组
for (var i in a) {  //遍历数组
    b.push(String.fromCharCode(a[i]));  //把每个字符编码都转换为字符串存入数组
}
console.log(b.join(""));  //返回字符串“读者您好”

You can pass all strings to fromCharCode() in order.

var b = String.fromCharCode(35835,32773,24744,22909);  //传递多个参数

You can also use the apply() method to dynamically call the fromCharCode() method.

var a = [35835,32773,24744,22909], b = [];
var b = String.fromCharCode.apply(null,a);  //动态调用fromCharCode()方法，并传递数组
console.log(b);  //返回字符串“读者您好”

fromCharCode() method is a static method of String type and cannot be called through a string. Contrary to the fromCharCode() method, the charCodeAt() method can convert a string to Unicode encoding.

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