Detailed introduction to JavaScript programming steps

JavaScript is a widely used programming language used to add interactivity and dynamic effects to web pages. It is a client-side scripting language that can run in a web browser to execute scripts including user interface behavior, data validation, dynamic rendering, animation effects, etc. The JavaScript language is simple, flexible, cross-platform, and widely used. It is an indispensable part of Web front-end development. The JavaScript programming steps will be introduced in detail below.

1. Basic syntax

The basic syntax of JavaScript includes variables, operators, conditional statements, loop statements, functions, objects, etc. You should be familiar with these basic syntax rules when writing JavaScript code so that you can use them correctly.

Declare variables: var or let

JavaScript has three types of variable declarations: local variables declared with var or let, constants or global variables declared with const.

Example:

var x = 10;

let y = 20;

const z = 30;

Conditional statement: if statement

The if statement is a basic conditional statement that is used to execute code branches based on conditions.

Example:

if (x%2 == 0) {

console.log("x is an even number");

} else {

console.log("x is an odd number");

}

Loop statement: for statement

The for statement is a basic loop statement. Use To execute a loop based on conditions.

Example:

for (var i = 0; i < 10; i ) {

console.log("The value of i is:" i);

}

2. Used in HTML pages

In HTML pages, we can use multiple script tags (<script>) to include JavaScript code . For example: </p> <p><script></p> <p>console.log("Welcome to JavaScript");</p> <p></script>

3. External JavaScript file

If the amount of JavaScript code is large, you can use an external JavaScript file. External files have a separate .js file extension and contain the entire JavaScript code.

Example:

(function() {

var x = "This variable is defined outside this function";

function displayX() {

console.log(x);

}

})();

4. Event Handler

JavaScript uses events to handle user interactions, e.g. Click buttons, enter text, etc. These events require event handlers to handle.

Example:

Display Date

5. AJAX

AJAX (Asynchronous JavaScript and XML) is a technology for creating fast and dynamic web applications. Using AJAX, front-end programmers can implement partial refreshes without having to reload the entire web page.

Example:

function loadDoc() {

  var xhttp = new XMLHttpRequest();

  xhttp.onreadystatechange = function() {

    if (this.readyState == 4 && this.status == 200) {

     document.getElementById("demo").innerHTML =

     this.responseText;

    }

  };

  xhttp.open("GET", "ajax_info.txt", true);

  xhttp.send();

}

The above are the basic steps and syntax rules of JavaScript programming. Although it may take some time to master them initially, mastering them correctly These techniques will enable you to create a variety of JavaScript interactive applications and help you write cleaner, more efficient, and more maintainable code.

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