How to use function in js

Functions in JavaScript can be reused. The usage is as follows: Function declaration: Use the function keyword to declare, receive parameters and return results. Function expressions: declared using const, receiving parameters and returning results using arrow notation (=>). Self-invoking functions: Declared using an immediately invoked function expression (IIFE), they execute immediately when defined. Class method: A method declared in the class definition, usually used on objects.

Function in JavaScript

A function in JavaScript is a block of code that can be reused and can pass parameters and return results.

Usage

Declaring functions

There are four ways to declare functions:

• Function declaration: function function name (parameter) {code block}
• Function expression: const function name = (parameter) => {code block}
• Self-calling function: (function() {code block})()
• Class method: class class name { method name (parameters) { code block } }

Calling a function

To call a function just use its name, followed by any parameters in parentheses:

<code class="javascript">函数名(参数1, 参数2);</code>

Parameters

The function can receive parameters, which are used as variables in the function body.

Return value

A function can return a value using the return keyword.

Example

Function declaration:

<code class="javascript">function sayHello(name) {
  return `Hello, ${name}!`;
}

const greeting = sayHello("Bob");
console.log(greeting); // 输出："Hello, Bob!"</code>

Function expression:

<code class="javascript">const multiply = (a, b) => {
  return a * b;
};

const product = multiply(10, 5);
console.log(product); // 输出：50</code>

Since Calling function:

<code class="javascript">(function() {
  console.log("立即执行！");
})();

// 输出："立即执行！"</code>

Class method:

<code class="javascript">class Person {
  constructor(name) {
    this.name = name;
  }

  greet() {
    console.log(`Hello, my name is ${this.name}!`);
  }
}

const person = new Person("Alice");
person.greet(); // 输出："Hello, my name is Alice!"</code>

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