An in-depth understanding of front-end DOM operations: basic concepts, methods and best practices

introduction

This article will delve into DOM operations in front-end development, including basic concepts, common methods, and best practices. Through clear and easy-to-understand explanations and practical case analysis, we will learn together how to use DOM operations most effectively to improve the user experience of front-end applications.

1. Introduction to DOM operations

Before we delve into DOM operations, we first need to understand what DOM is. DOM (Document Object Model) is a programming interface that converts a web page into a structured tree diagram, allowing developers to dynamically access and modify the content, structure, and style of the web page.

DOM operations mainly involve the following types:

1. Element operations: You can add, delete, modify or find HTML elements through DOM operations. For example, you can use document.getElementByIdthe method to obtain an element with a specified ID and modify the content of the element using element.innerHTMLthe method.
2. Attribute operations: You can read or set attributes of HTML elements through DOM operations. For example, you can use to element.getAttributeget an element's properties and use element.setAttributeto set an element's properties.
3. Style manipulation: You can modify the CSS style of an element through DOM manipulation. For example, you can use element.style.colorfont to change the font color of an element.
4. Event operations: You can register, deactivate or listen for events through DOM operations. For example, you can use element.addEventListenermethods to add event listeners to elements.

2. Best practices for front-end DOM operations

In front-end development, reasonable DOM operations can significantly improve user experience and performance. Below, we will introduce some optimization tips and best practices for DOM operations.

1. Minimize DOM operations: Frequent DOM operations will cause the browser to perform a large number of redraws and reflows, thus affecting performance. Therefore, DOM operations should be minimized, for example, by modifying the style once instead of resetting it every time you need to change the style.
2. Use document fragments for batch operations: If you need to insert multiple nodes, consider using document fragments (DocumentFragment). It removes nodes from the document and then inserts them into the document all at once after completing the batch operation, which reduces the number of DOM redraws and reflows.
3. Using event delegation: Event delegation is a technique that adds event listeners to parent elements and then filters events based on the uniqueness of child elements. This can achieve the effect of event processing without adding separate event listeners for each child element.
4. Use virtual DOM technology: Virtual DOM is a technology that encapsulates real DOM operations in JavaScript objects. By comparing the differences between virtual DOM and real DOM, you can find out the parts that need to be truly modified, and then perform minimized DOM operations. This can greatly improve performance.
5. Avoid using DOM operations with layout functions: Some DOM operations will trigger browser redrawing and reflow, such as changing the offsetHeight, offsetWidth, scrollLeft, scrollTop and other attributes of elements. These operations will significantly affect page performance. Therefore, these operations should be avoided in performance-sensitive situations.
6. Use requestAnimationFrame for animation rendering: requestAnimationFrame is an API provided by the browser. It can execute a set of animations before the next redraw. This allows animation rendering to be placed in the browser's optimization thread to improve the smoothness of the animation.

3. Case analysis and practical code

In order to illustrate how the best practices of DOM manipulation can be applied in specific projects, we will demonstrate through a simple example. Suppose we need to implement a function that dynamically changes the width of table columns... (Omit 1,000 words here)

In this example, we will show how to use event delegation to handle multiple column width change events in a table. First, we need to create an event listener that will be triggered when the user clicks on a column header. Then, we need to get the width of the column that the user clicked in the event handler and dynamically set the width of this column. Finally, we want to compare the performance difference between using event delegation and using traditional event binding.

Here is a simple JavaScript code example:

// 获取所有的列头元素
let headers = document.querySelectorAll('th');

// 为每一个列头元素添加点击事件监听器
for (let i = 0; i < headers.length; i++) {
    
    
  headers[i].addEventListener('click', function() {
    
    
    // 获取当前点击的列头元素的宽度
    let width = this.offsetWidth;
    // 动态设置这个列的宽度
    this.style.width = width + 'px';
  });
}

In the above code, we first document.querySelectorAllobtain all the column header elements through the method, and then add a click event listener for each column header element through a for loop. In the event handling function, we first obtain the width of the currently clicked column header element, and then dynamically set the width of this column.

4. Summary

Through the introduction of this article, we have a detailed understanding of the basic knowledge, common methods and best practices of DOM operations. By reducing DOM operations and using technologies such as document fragments, event delegation, and virtual DOM, front-end performance and user experience can be effectively improved. I hope this article can help everyone better understand and apply DOM operations and bring more possibilities to our front-end development.