Does javascript automatically execute functions?

JavaScript is a powerful programming language that is widely used to create interactive user interfaces for websites and applications. In JavaScript, there is a concept called "auto-execution function", which allows some code to be executed automatically when JavaScript is loaded without the need to trigger it manually.

Automatically executed functions are often called IIFE (Immediately Invoked Function Expression) or self-executing functions. It is a function expression that immediately calls itself and returns the result. This function may contain any JavaScript code and is executed immediately when the script is loaded. During this process, the code within the function will be protected within its own scope. This ensures that variables and functions defined within the function do not affect other code in the global scope.

Here is a simple example that demonstrates how to use IIFE to automatically call a function on load:

(function() {
   console.log("这个自动执行函数被调用了");
})();

This code block is composed of two parts. First, a function is defined. This function has no name and is called an anonymous function. Anonymous functions are enclosed in parentheses to convert the function into a function expression. This is key to achieving automation. In the parentheses following the function definition, we immediately call the function. This way, the function will be executed immediately after being defined. In this example, the console will output "This autoexecution function was called."

Another important feature of this pattern is that all variables and functions created within the function are encapsulated in a new scope. This means that variables inside a function are not visible to external code and can only be used inside the function. This way we avoid global name conflicts and ensure the code is more secure and maintainable.

IIFE is often used to modularize code and break the code into smaller chunks. It also helps us improve performance as it prevents variables and functions from being added to the global scope. This reduces naming conflicts and the number of global variables, thereby improving application performance.

In JavaScript, IIFE is a very useful tool that allows us to automatically execute some code when the code is loaded, and the variables and functions defined internally will not interfere with the global scope. If you are building a JavaScript application or website, consider using IIFE to organize and protect your code.

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