Learn to Code With JavaScript: Part 4, Functions

JavaScript function: no return value function and return value function

This article discusses two types of functions in JavaScript: void functions and value-returning functions.

Void Functions (Void Functions)

The no return value function performs a series of operations, but does not return any value. They are often used to perform side effects, such as printing out or modifying global state.

The basic structure of the

function is as follows:

function functionName() {
    语句;
    语句;
    // ...
}

A sample of a function without return value:

function greet() {
    console.log("Hello, World");
}

Methods to call a function (also known as executing a function or calling a function):

greet();

It is worth noting that even the function without return value returns implicitly returns undefined. The following is the greet function represented by the arrow function:

let greet = () => console.log("Hello, World");

Example of function with parameters:

let greet = name => console.log(`Hello, ${name}`);

// 输出：Hello, Monty
greet("Monty");

let greet = (fname, lname) => console.log(`Hello, ${fname} ${lname}. How are you?`);

// 输出：Hello, Monty Shokeen. How are you?
greet("Monty", "Shokeen");

let greet = (fname, lname) => {
    let name = `${fname} ${lname}`;
    console.log(`Hello, ${name}`);
};

// 输出：Hello, Monty Shokeen
greet("Monty", "Shokeen");

The arrow function is an anonymous function and is named by assigning values ​​to variables. One of the advantages of arrow functions is to make the code more concise.

Example of a factorial function without a return value:

function factorial(x) {
    let result = 1;
    while (x > 1) {
        result *= x;
        x -= 1;
    }
    console.log(result);
}

// 输出：3628800
factorial(10);

// 输出：479001600
factorial(12);

// 输出：6402373705728000
factorial(18);

Value-Returning Functions

There is a return value function performs a series of operations and returns a value. The function must end with a return statement. The following example returns the sum of two numbers:

function add(x, y) {
    return x + y;
}

General form of return value function:

function functionName() {
    语句;
    语句;
    // ...
    return 表达式;
}

The

function returns the value of the expression. Such functions are useful when you need to store the return value in a variable or use it elsewhere in your code. If you plan to use the value of a function elsewhere in your code, you should explicitly return the value from the function.

Example of a factorial function with a return value:

function factorial(x) {
    let result = 1;
    while (x > 1) {
        result *= x;
        x -= 1;
    }
    return result;
}

// 输出：3628800
console.log(factorial(10));

// 输出：479001600
console.log(factorial(12));

// 输出：6402373705728000
console.log(factorial(18));

The output result of

is the same as the function without return value, the difference is that the return value is output by console.log. The function with return value returns a value, while the function without return value returns undefined.

Scope (Scope)

Scope refers to the area in the program where variables can be accessed. Variables declared inside a function (including function parameters) are local variables. Code blocks also have scopes in which local variables can be created.

Variables not declared in code blocks or modules are global variables. If global variables are required, global constants can be used. Otherwise, you should try to limit the code to the module because the module has its own scope. A better way is to use modules to organize the code so that the code structure is clear.

This article was updated with Monty Shokeen. Monty is a full-stack developer who loves writing tutorials and learning new JavaScript libraries.

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