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How to write javascript

PHPz

Release： 2023-04-24 09:43:28

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JavaScript is an essential part of web development. It can add dynamic effects, interactive features to the website and add or modify content on the page. In this article, we will discuss how to write JavaScript code from scratch.

Introduce JavaScript files

First, introduce JavaScript files into the HTML document. Generally speaking, the following elements should be added to the tag of the HTML file:

<head>
  <script src="path/to/javascript-file.js"></script>
</head>

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"path/to/javascript-file.js" should be replaced with your actual file storage path and file name.

Declaring variables and functions

Before writing JavaScript code, you first need to declare variables and functions. You can use the var keyword to declare variables, for example:

var a = 5;
var b = 'hello world';

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The way to declare a function is also very simple:

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

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Note that in JavaScript, a function can also be regarded as a variable.

Control flow

There are three control flow structures in JavaScript: if statement, for loop and while loop.

The if statement is used to execute different codes based on conditions:

if (x > 5) {
  console.log('x is greater than 5');
} else {
  console.log('x is less or equal to 5');
}

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The for loop is used to repeatedly execute the code n times:

for (var i = 0; i < n; i++) {
  console.log(i);
}

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The while loop is used when the condition is true Repeatedly execute code when:

while (x < 5) {
  console.log(x);
  x++;
}

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Event monitoring

A powerful feature of JavaScript is the ability to respond to user operations by listening to events. Common events include mouse clicks, keyboard keystrokes, and form submissions. The following is an example of binding a click event:

var el = document.getElementById('myButton');
el.addEventListener('click', function() {
  console.log('button clicked');
});

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In this example, we get an element object with the id "myButton" on the page and attach the callback function with the "click" event to its click on events.

Operation DOM

JavaScript can not only listen to events, but also operate DOM nodes on the page. By getting a reference to an element, we can change the element's style, text, or attributes, etc. Here is an example of changing the text of an element:

var el = document.getElementById('myElement');
el.innerHTML = 'new text';

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In this example, we get the element object and set its innerHTML property to the new text content.

Summary

With the above method, you can write JavaScript code from scratch. However, these are just the basics of JavaScript. The best way to learn JavaScript is to write a lot of code and try to solve problems when you encounter them while programming. In this way, you will gradually become familiar with JavaScript concepts, language structures, and best practices, making you an excellent web development engineer.

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