What are JavaScript Functions? A Beginners Guide to Writing And Using Them.

JavaScript functions are powerful tools in programming, whether you are building a simple calculator or a complex web application, functions are essential. This article will gradually explain the basic knowledge of JavaScript functions to help you easily master the writing and use of functions.

What is a function?

A function is a block of code that performs a specific task. Once written once, it can be called repeatedly when needed, improving code reusability.

How to write a function?

Let’s write our first function step by step:

<code class="language-javascript">function greet() {
  console.log("Hello, world!");
}
greet();</code>

Code explanation:

• function: keyword for declaring functions.
• greet: Function name (any descriptive name can be used).
• (): Parameter list (empty here means the function does not require any input).
• {}: Function body, containing the code for function execution.

Call the greet() function and the console will output "Hello, world!".

Parameters and parameter values

Parameters make functions more flexible. Parameters are variables declared when the function is defined, and parameter values ​​are the actual values ​​passed to the parameters when the function is called.

<code class="language-javascript">function greet(name) {
  console.log(`Hello, ${name}!`);
}
greet("Majeedat");</code>

Output: Hello, Majeedat!

The difference between parameters and parameter values:

• Parameters: Placeholders defined when the function is declared.
• Parameter value: The actual value passed to the parameter when the function is called.

Return value

Function can not only output information, but also return a value.

<code class="language-javascript">function add(a, b) {
  return a + b;
}
let result = add(5, 3);
console.log(result); // 输出：8</code>

The

return keyword returns the calculation result to the place where the function is called.

Function expression

Another way to define a function is a function expression:

<code class="language-javascript">const greet = function(name) {
  console.log(`Hi, ${name}!`);
};</code>

Assign the function to a variable.

Arrow function

Arrow functions are a more concise way to define functions:

<code class="language-javascript">const greet = (name) => {
  console.log(`Hey, ${name}!`);
};</code>

For single-line functions, the curly braces can be omitted:

<code class="language-javascript">const add = (a, b) => a + b;
console.log(add(2, 4)); // 输出：6</code>

Advantages of functions

1. Reusability: Write once, use many times.
2. Readability: Make the code clearer and easier to understand.
3. Modularization: Break code into small, manageable modules.

Common mistakes made by beginners

A. Forgot to call function: Define a function but forget to call it.

<code class="language-javascript">function greet() {
  console.log("Oops, you forgot to call me!");
}
// 需要调用 greet();</code>

B. Parameter mismatch: The number of parameters expected by the function does not match the number of parameters actually passed.

<code class="language-javascript">function add(a, b) {
  return a + b;
}
console.log(add(5)); // 输出：NaN (Not a Number)</code>

C. Infinite Loop: The function itself is called infinitely recursively.

Summary

JavaScript functions are the basis for building dynamic interactive web applications. Proficient in using functions will greatly improve your programming efficiency. Start writing your own functions now!

Author: MJ Goodbye!

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