How to create a function `generateSelector` to generate a CSS selector path for a DOM element?-CSS Tutorial-php.cn

How to create a function `generateSelector` to generate a CSS selector path for a DOM element?

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Release： 2023-09-20 18:17:11

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如何创建一个函数 `generateSelector` 来生成 DOM 元素的 CSS 选择器路径？

The generateSelector method is a useful tool for determining the path to a specific part of a website, called a DOM element. Understanding how CSS selectors work and how to build them can be useful in a variety of situations, such as test automation or building shortcuts for easily selecting elements. In this article we will discuss the concept of this function and provide clear examples of how to use it.

Suppose you want to change a specific element on your website. But how do you know which selector to use? This is where our generateSelector function comes in! This function will get a specific element on the website and give us a selector we can use to change it.

Understanding CSS Selectors

Before we delve into the creation of the generateSelector function, it is crucial to understand what a CSS selector is and the principles behind its operation.

CSS selectors are patterns used to select HTML elements on a page that require styling. They are a fundamental aspect of CSS style sheets, serving as a means of applying styles to specific elements.

Example

The following CSS rule utilizes a selector to target all

elements on the page and assigns the style property of color to red -

<!DOCTYPE html>
<html>
<head>
   <style>
      p {
         color: red;
      }
   </style>
</head>
<body>
   <p>This text will be red.</p>
</body> 
</html>

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Example

The p in CSS rules is the selector. CSS selectors can be much more complex than an element's tag name. They can be used to select elements based on their class, ID, attribute values, etc. For example -

<!DOCTYPE html>
<html>
<head>
   <style>
      #main-header {
         background-color: blue;
      }
   </style>
</head>
<body>
   <header id="main-header">
      <h1>My website</h1>
   </header>
   <!-- other content here -->
</body>
</html>

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This CSS rule selects the element with the ID "main-header" and applies the "backgroundcolor: blue" style to it.

Create generateSelector function

Introducing the concept of CSS selectors (CSS selectors are a method of identifying and positioning specific elements in web pages to achieve styling), we can now continue to create the generateSelector function. The function will accept a DOM (Document Object Model) element as input and in return it will provide the CSS selector path for that specific element.

grammar

function generateSelector(element) {
   let selectors = [];
}

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First, we will start an empty array called "selector". This array will act as a container for the selectors we generate for a given DOM element when traversing and inspecting its ancestor elements.

grammar

while (element) {
   let selector = '';
   if (element.tagName === 'HTML') {
      selector = 'html';
   }
}

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When we iterate over each ancestor, we will generate a selector for it. We first check if the element is an element. If so, we will add the string "html" to the selector variable

For all other elements we will check if the element has an ID. If so, we will use the ID as the selector. If not, we will use the element's tag name and its class name as the selector.

grammar

else {
   if (element.id) {
      selector = '#' + element.id;
   } else {
      selector = element.tagName.toLowerCase();
      if (element.className) {
         selector += '.' + element.className.replace(/\s+/g, '.');
      }
   }
}

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After generating the selector, we add it to the selector array and move to the next ancestor by setting element equal to element.parentNode.

grammar

selectors.unshift(selector);{
   element = element.parentNode;
}

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Finally, we will use the join() method to join all selectors in the selector array and return the resulting CSS selector path as a string.

grammar

return selectors.join(' > ');{
}

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Use generateSelector function

Now that we have implemented the generateSelector function, let's see how to use it in practice.

For example, let's say you have the following HTML -

<!DOCTYPE html>
<html>
<body>
   <div id="myDiv">
      <p>Hello World</p>
   </div>
   <div id="result"></div>
   <script>
      function generateSelector(element) {
         let selectors = [];
         while (element) {
            let selector = '';
            if (element.id) {
               selector = '#' + element.id;
            } else {
               selector = element.tagName;
            }
            selectors.unshift(selector);
            element = element.parentNode;
         }
         return selectors.join(' > ');
      }
   </script>
   <script>
      window.onload = function(){
         
         // Select the <p> element and get its CSS selector path
         const p = document.querySelector("p");
         if(p!==null){
            const selector = generateSelector(p);
            document.getElementById("result").innerHTML = selector;
         }
         else{
            console.log("Error : Element not found");
         }
      }
   </script>
</body>
</html>

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It's important to note that this is just an example and the selector will vary depending on the elements and HTML structure you pass to the function.

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