IIFE Use Cases: Immediately Invoked Function Expressions In Action

The functional expression (IIFE) immediately called, also known as the self -execution function, is a code block defined and executed immediately after creation. Internal functions can use keywords (traditional methods) or arrow functions. In any way, the entire function is included in a pair of brackets, and then with a pair of brackets. This second pair of brackets is to call the operator, which allows the function to execute immediately.

function Traditional grammar that uses the function declaration:

Arrow function syntax:

(
    function () {
        console.log('IIFE called');
    }
)();

Now we know what is IIFE, and the next question is why it is useful? The following are some cases: <用>

(
    () => console.log('IIFE with arrow function called')
)();

By creating a new scope to avoid pollution, global naming space

Create closures with private variables
Used to perform asynchronous and waiting functions
The creation of the module
• In fact, a large part of my daily work is to use Puppeteer to perform automated testing. These Puppeteer scripts are huge IIFE (usually thousands of presidents), which run the code of the test application user interface (UI). In any case, let's continue to discuss our use cases.

Avoid the global naming space of pollution

What does this mean? It essentially means a conflict between the name between the global variables and the local variable of the same name. This becomes more obvious in large enterprise applications. In large enterprise applications, the possibility of reusing variable names will increase, especially when multiple developers handle the same application. The following example illustrates this.

After executing this code, the output is as follows:

// 全局作用域
const value = "此变量位于全局作用域中，名为 'value'。";
const stateLocation = () => console.log("现在位于全局作用域");

stateLocation();
console.log(value);
console.log("*********************************************************");

(
    function () {
        // 函数作用域
        const value = "此变量位于函数作用域中，即使重用了变量名 'value'，也避免了全局污染";
        const stateLocation = () => console.log("现在位于 IIFE 的函数作用域");

        stateLocation();
        console.log(value);
    }
)();

Create closures with private variables

<code>现在位于全局作用域
此变量位于全局作用域中，名为 'value'。
*********************************************************
现在位于 IIFE 的函数作用域
此变量位于函数作用域中，即使重用了变量名 'value'，也避免了全局污染</code>

Looking back, closing is an internal function that can access variables in the external function scope. This IIFE example of this calculation circular area illustrates this. In addition, the variables in external functions are private because it cannot be accessed outside the function.

Output: <<>

const areaOfCircle = (
    function () {
        const pi = Math.PI; // 私有变量
        return function (radius) { // 具有访问外部作用域私有变量的闭包
            return pi * (radius ** 2);
        };
    }
)();

const areaWithRadius2 = areaOfCircle(10);
console.log('半径为 10 的圆的面积是', areaWithRadius2);
// console.log('PI = ', pi); // ReferenceError: pi is not defined

Used to perform asynchronous and waiting functions

IIFE can also be used to perform asynchronous operations, such as network calls. The following examples obtain the list of the items to be obtained from the analog server.

<code>半径为 10 的圆的面积是 314.1592653589793</code>

The creation of the module

This is a module using basic physical equations. It can be exported and used by other programs. I will discuss this further in another article "Using the IIFE Module mode to build a command line physical computing application". Please pay attention to the use of private variables and closures.

(
    async function () {
        const response = await fetch('https://dummyjson.com/todos');
        const todosObject = await response.json();
        const todoList = todosObject.todos.map(todo => todo.todo);
        console.log(todoList);
    }
)();

It can be seen that IIFE has countless use cases. It can improve the security of data by packaging data and adding modularization to applications.

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