Several common JavaScript functions and their usage

JavaScript is a popular programming language with a wide range of applications, especially in web development. JavaScript functions are one of its core features. Through functions, we can modularize code, achieve code reuse and simplify code structure. In this article, I will introduce several common JavaScript functions and their usage.

1. Function definition and calling

In JavaScript, the definition of a function is very simple and straightforward. We can use the function keyword to define a function and assign it to a variable, that is, declare a function variable. For example:

var add = function(a, b) {
  return a + b;
}

console.log(add(1, 2)); // 输出：3

In the above example, we defined a function variable named add and assigned it as a function that accepts two parameters a and b. The return value of the function is their sum. When calling a function, we just call it like a normal variable.

2. Immediately Invoked Function Expression

Immediately Invoked Function Expression (IIFE) is a common way of defining and calling functions. Its function is to execute the function immediately after declaring it, thereby forming an independent scope and avoiding global variable pollution and function name conflicts. For example:

(function() {
  var message = "Hello world!";
  console.log(message);
})();

In this example, we use an IIFE to declare and call an anonymous function, which defines a local variable named message and assigns it the value "Hello world!". After the IIFE execution is completed, the message variable will be destroyed and no longer exists in the current scope.

3. Recursive function

A recursive function refers to a function that calls itself inside the function. Recursive functions are widely used, especially in tree structure traversal, sorting and other operations, and are often the best solution. For example:

function factorial(n) {
  if (n === 0 || n === 1) {
    return 1;
  } else {
    return n * factorial(n - 1);
  }
}

console.log(factorial(5)); // 输出：120

In this example, we define a recursive function called factorial that calculates the factorial of a given positive integer n. In the function, if n is 0 or 1, 1 is returned; otherwise, the factorial function is called recursively to calculate the factorial of n-1 and returns the product of n and the result.

4. Arrow function

The arrow function is a new function definition method in ES6. It has a more concise and clear syntax form and can usually replace the traditional function definition method. For example:

var multiply = (a, b) => a * b;

console.log(multiply(2, 3)); // 输出：6

In this example, we define an arrow function named multiply to calculate the product of two parameters a and b. The definition form of arrow function is to connect the parameter list and function body with "=>". If the function body has only one line of code, you can omit the curly braces and the return keyword and directly return the result of that line of code; otherwise, you need to wrap the function body with curly braces and use the return keyword to return the result.

Conclusion

The above four JavaScript functions are common function types in Web development. They each have different characteristics and usages and can be used flexibly according to actual development needs. When writing JavaScript functions, we should follow good coding habits, try to make the code structure clear and concise, and improve the readability and maintainability of the code.

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