What do domain chains and closures do?

Domain chain and closure are important concepts in JavaScript, which can help us manage the scope of variables and implement advanced programming skills: 1. Domain chain refers to the scope created through function nesting in JavaScript Hierarchy, whose function is to determine the order in which variables are searched and accessed in the code; 2. Closure, which means that a function can access and save variables in its lexical environment, and can still maintain references to these variables even after the function execution ends. .

# Operating system for this tutorial: Windows 10 system, Dell G3 computer.

Scope Chain and Closure are important concepts in JavaScript. They can help us manage the scope of variables and implement advanced programming techniques. Below I will explain their role:

Scope Chain

Scope chain refers to the scope hierarchy created through function nesting in JavaScript. Its role is to determine the order in which variables are found and accessed in the code. When a variable is accessed, the JavaScript engine searches for the variable's value along the scope chain from the inside out until it finds the first matching variable or reaches the global scope. The functions of the domain chain are as follows:

1. Variable search: The domain chain determines the search order of variables in the code, ensuring that variables can be accessed and used within the correct scope.
2. Scope maintenance: Domain chain maintains the scope relationship created by function nesting, allowing internal functions to access variables of external functions.
3. Scope isolation: Domain chain limits the scope of variables, avoids naming conflicts between variables, and improves the reliability and maintainability of the code.

Closure (Closure)

Closure means that a function can access and save the variables in its lexical environment, and can still maintain access to these variables even after the function execution ends. Quote. The functions of closures are as follows:

1. Data privatization: Through closures, private variables can be created, making the variables inaccessible to the outside, realizing a kind of data encapsulation and hiding.
2. Extension of variable life cycle: Closure can make local variables still exist after the function execution ends, extending the life cycle of variables and avoiding being recycled by the garbage collection mechanism.
3. Save state: Through closure, the function can continuously save the state of its lexical environment, achieving a memory effect for continued use in subsequent calls.

Closures are widely used in many scenarios in JavaScript, such as modular development, event processing, asynchronous programming, etc. It can provide a more flexible and efficient programming method, making the code more readable and maintainable. But at the same time, unreasonable use of closures may also lead to memory leaks and other problems, so it needs to be used with caution.

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