What is const used to define in js

The const keyword in JavaScript is used to declare constants, that is, immutable data types. The const declaration must be initialized to a value that: 1. Prevents accidental changes and improves code reliability; 2. Improves code readability; 3. Avoids memory leaks. It is recommended for data that will not change, such as physical constants, enumeration values, functions and object property names.

The purpose of const keyword in JavaScript

const is the keyword used to declare constants in JavaScript. A constant is an immutable data type, which means it cannot be reassigned after declaration.

Usage of const

• When you declare a constant using the const keyword, it must be initialized to a value. For example:

<code class="javascript">const pi = 3.141592653589793;</code>

• Once declared, a constant cannot be reassigned. Attempting to reassign will result in an error:

<code class="javascript">const pi = 3.141592653589793;
pi = 4; // 导致错误</code>

Advantages of const

Using const has the following advantages:

• Prevent accidental changes: Constants ensure that critical data is not accidentally modified, improving the reliability of the code.
• Improve code readability: By using const, you can clearly indicate that the value of a variable cannot be changed, making the code easier to understand.
• Avoid memory leaks: Constants are stored in the engine's constant pool and will not occupy the memory heap, thereby reducing the risk of memory leaks.

Best Practices

It is recommended to use const in the following situations:

• Physical constants (such as pi)
• Enumeration values
• Function and object property names
• Any other data that will not be changed

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