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The content of this article mainly focuses on the data types of ECMAScript. The content of the article is clear and well-organized. It is very suitable for beginners to learn and is worth reading. Interested friends can follow the editor to read together. I hope you can get something through this article!

ECMAScript data types are divided into two types: 1, basic data types, including String, Number, Boolean, undefined, null and Symbol types; 2, reference data types, including Object, Function and Array types.

The operating environment of this tutorial: windows7 system, ECMAScript version 6, Dell G3 computer.

ECMAScript data types can be divided into two types: basic data types and reference data types

Basic type

The basic type is also called the value type.

String: any string

Number: any number

Boolean:true 、 false

Undefined:undefined

Null:null

Symbol

Object Typ

An object type is also called a reference type

Object: any object

Function: a special object (difference from Object: executable)

Array: a special object (numerical subscript, internal data is ordered)

How to judge the type of data

Typeof: can judge undefined, numeric value, string, Boolean value, function

Unable to judge: null and Object, Object and Array

Returns a string representation of the data type.

Instanceof: determines the specific type of object.

=: undefined and null can be judged.

1. The method of judging the basic types:

Var assuredly console.log (a); / undefinedconsole.log (typeof a); / / "undefined" console.log (a===undefined); / truea=4;console.log (typeof astatine = "number"); / / truea='dewferf';console.log (typeof astatory isolation stringing`); / / trueconsole.log (typeof astaturitystring`); / / falsea=true;console.log (typeof axiomorphology 'boolean'); / / truea=null;console.log (typeof acentology); / / "object", true

2. The judgment method of citation type.

Var b1 = {b2: [1 b3:function () {console.log ('b3'); return function () {return' lxyxxx';}; console.log (typeof b1.b2); / / 'object'console.log (b1 instanceof Object,b1 instanceof Array); / / true,falseconsole.log (b1.b2 instanceof Array,b1.b2 instanceof Object) / / true,trueconsole.log (b1.b3 instanceof Function,b1.b3 instanceof Object); / / true,trueconsole.log (typeof b1.b3); / / 'function'console.log (typeof b1.b3 =' function'); / / trueconsole.log (typeof b1.b2 [2]); / / 'function'console.log (typeof b1.b2 [2] =' function'); / / trueb1.b2 [2] (4); / / because b1.b2 [2] is a function, b1.b3 () () is executed; / /

Symbol Typ

Symbol is a new data type introduced in ECMAScript6, which represents a unique value. Values of type Symbol need to be generated using the Symbol () function, as shown in the following example:

Var str = "123"; var sym1 = Symbol (str); var sym2 = Symbol (str); console.log (sym1); / / output Symbol (123) console.log (sym2); / / output Symbol (123) console.log (sym1 = = sym2); / / Export false: although sym1 and sym2 look the same, they are actually different. Sym1 and sym2 are unique according to the characteristics of Symbol types.

The parameters of the Symbol function only represent a description of the current Symbol value, so the return values of Symbol functions with the same parameters are not equal.

You cannot use the new command before the Symbol function, otherwise an error will be reported. This is because the generated Symbol is a primitive type value, not an object. That is to say,

Attributes cannot be added because the Symbol value is not an object. Basically, it is a data type similar to a string.

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