How to use custom functions in javascript

JavaScript is a very popular programming language that provides many different tools and features that enable developers to build efficient and easy-to-maintain code. One of them is a custom function, which is a user-defined block of code that can be called and used multiple times in a program. In this article, we will take a deep dive into how to use custom functions in JavaScript and what the rules are for defining functions.

1. What is a custom function

In JavaScript, a function is a reusable block of code that consists of a set of statements designed to achieve a specific task. Think of a function as a template that accepts inputs (parameters) and returns outputs. Create a function, name it whatever you want, and tell it what it needs to do. Functions in JavaScript are defined by the function keyword.

The general function definition syntax is as follows:

function functionName(parameters) {
  //函数内的代码
  return value;
}

Among them, functionName is the name of the function, parameters is the list of input parameters, the statement block is the code block, and the return statement indicates the output value of the function .

Within a function, you can do anything from simple calculations to manipulating the DOM or calling APIs. The power of custom functions is that they can be used as independent units of code to support more complex programs.

2. How to use custom functions

Using custom functions requires following the following steps:

Step 1: Define the function

As mentioned above, Defining functions in JavaScript requires the use of the function keyword. First you need to name the function and define the input parameter list. Then you need to describe what the function does inside the function. The rule to remember is that a function definition statement does not execute the function. The inner JavaScript code will only be executed when the function is called.

Sample code:

function add(num1, num2) {
 return num1 + num2;
}

This custom function is named "add", requires two parameters "num1" and "num2", and returns the sum of their two numbers.

Step 2: Call the function

To call a function, simply name the function and provide the required parameters. As shown in the figure below, when calling a function in JavaScript, pass the custom function name and required parameters as parameters to the function.

let result = add(2, 3);

In this example, parameters 2 and 3 are passed to the function add. The function returns the sum 5, which is stored in the variable result.

3. Rules for Custom Functions

In JavaScript, there are several rules that need to be remembered in order to correctly define custom functions and their input parameters and statements. Here are some rules for writing JavaScript custom functions:

1. The function name must be a valid tag name. Be sure not to name functions with reserved words. Reserved words are keywords with special meaning in JavaScript.
2. If the function requires input parameters, they must be specified within parentheses. When multiple parameters are present, they are separated by commas.
3. If the function returns a value, it must be specified using the return statement. If the function does not specify a return value, it returns undefined.

With these rules, you can start writing JavaScript custom functions.

Summary

Through the discussion of JavaScript custom functions, we learned what custom functions are and how they are used. Custom functions can encapsulate code into reusable chunks and support more complex programs. In order to write custom functions correctly, basic rules need to be followed to ensure correctness and execution capabilities.

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