What are the basic data types in javascript

The basic data types of JavaScript are: null (null value), undefined (undefined value), number (number), string (string), boolean (Boolean value), object (object).

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

JavaScript defines 6 basic data types, as shown in the table:

Basic data types of JavaScript

Data type	Description
null	Null value means non-object
undefined	Undefined value, indicating an unassigned initialization value
number	Number, the value of mathematical operation
string	String, representing information flow
boolean	Boolean value, the value of logical operation
object	Object, representing a data set with a composite structure

You can use the typeof operator to detect the basic structure of the data type.

Example 1

The following code uses the typeof operator to detect the types of common values.

console.log(typeof 1);  //返回字符串"number"
console.log(typeof "1");  //返回字符串"string"
console.log(typeof true);  //返回字符串"boolean"
console.log(typeof {});  //返回字符串"object"
console.log(typeof []);  //返回字符串"object"
console.log(typeof function(){});  //返回字符串"function"
console.log(typeof null);  //返回字符串"object"
console.log(typeof undefined) ;  //返回字符串"undefined"

Note:

The typeof operator returns one of the six basic types in the form of a string. However, through comparison, it can be found that there are two differences between the typeof return value and the above table. Brief explanation As follows:

Classify null as the Object type, rather than as a value of a special type (Null).

Classify function(,){} as Function type. That is, the function is regarded as an independent basic data type, rather than a special subclass of the Object type.

Example 2

Since the return type of null value is Object, using the following custom function can avoid the impact of null value on basic type detection.

//如果是 null 值，则先返回字符串 "null" 否则返回（typeof o）的值
function typeOf(o){
    return (o === null) ? "null" : (typeof o);
}
console.log(typeOf(1));  //返回字符串"number"
console.log(typeOf("1"));  //返回字符串"string"
console.log(typeOf(true));  //返回字符串 "boolean"
console.log(typeOf({}));  //返回字符串"object"
console.log(typeOf(null));  //返回字符串"null"
console.log(typeOf(undefined));  //返回字符串"undefined"

In JavaScript, a function is a special structure. It can be a collection of code, or a data type; it can be used as an object, or it can be used as a constructor to create a type. The usage of JavaScript functions is relatively flexible, which is also a manifestation of the agility of the JavaScript language (functional programming).

[Recommended learning: javascript advanced tutorial]

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