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This article mainly explains the "es6 definition of const attributes can be changed", the article explains the content is simple and clear, easy to learn and understand, the following please follow the editor's ideas slowly in-depth, together to study and learn "es6 in the definition of const attributes can be changed" it!

Definition of constt

Const is used to define constants, and must be initialized at the time of definition, and cannot be modified after definition.

This is for basic types of data: an error will be reported if the value is not initialized when defined, and the error content is that it is not initialized. And variables of the basic data types defined by const really cannot be modified. For example:

1. Non-initialization

ConstPI

/ / UncaughtSyntaxError:Missinginitializerinconstdeclaration

2. Modification of variables

ConstPI=3.14159

PI=3

UncaughtTypeError:Assignmenttoconstantvariable.

The properties defined by const above are variable and are specific to objects or arrays. For example:

1. Const definition object:

ConstObj= {}

Obj.name= "fly63"

Console.log (Obj.name); / / print fly63

2. Const definition array

Arr= [3,4]

Arr [0] = 1

Console.log (Arr) / / output [1pm 4]

/ / No direct assignment is allowed, but wrong return: UncaughtTypeError:Assignmenttoconstantvariable.

Arr= [1,4]

What causes it? This is because the object or array belongs to the reference data class.

How to modify const

What const actually guarantees is not that the value of the variable cannot be changed, but that the data stored in the memory address that the variable points to shall not be changed.

For simple types of data (numeric, string, Boolean), the value is stored at the memory address that the variable points to, so it is equivalent to a constant. But for the compound type of data (mainly objects and arrays), the memory address that the variable points to is only a pointer to the actual data. Const can only guarantee that the pointer is fixed (that is, it always points to another fixed address). As for whether the data structure it points to is variable, it is completely out of control. Therefore, you must be very careful when declaring an object as a constant.

Thank you for your reading, the above is the content of "can the properties of const definition in es6 be changed?" after the study of this article, I believe you can change the attributes of const definition in es6 have a deeper understanding of this problem, the specific use of the situation also needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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