Advanced front-end programming: Master the is and where selectors to achieve complex effects

Advanced front-end programming: Master the is and where selectors to achieve complex effects

In front-end development, mastering advanced selectors is a very important skill. In addition to the common basic selectors such as id, class, tag, etc., the is() and where() selectors can help us achieve more complex effects. This article will introduce the usage of is() and where() selectors and provide some practical code examples.

1. is() selector

The is() selector is used to determine whether an element meets the specified selector conditions. It returns a boolean value that returns true if the element matches the selector criteria, false otherwise.

The syntax for using the is() selector is as follows:

$(selector).is(filter)

Among them, selector is the selector of the element we want to judge, filter is the conditional selector we want to judge.

The following is a simple example:

HTML code:

<div class="box">我是一个div元素</div>
<button>判断是否为box类</button>

JavaScript code:

$("button").click(function(){
  var result = $(".box").is(".box");
  if(result){
    alert("该元素是box类");
  } else{
    alert("该元素不是box类");
  }
});

When the button is clicked, the corresponding prompt box will pop up , tells us whether the div element has a box class. In this example, the is() selector returns a Boolean result by determining whether it has the .box class.

2. Where() selector

The where() selector can filter elements based on one or more conditional selectors. It returns a new jQuery object containing elements matching all criteria selectors.

The syntax for using the where() selector is as follows:

$(selector).where(filter1, filter2, ...)

Among them, selector is what we want to filter The element selectors, filter1, filter2, etc. are the conditional selectors we want to pass in.

The following is an example:

HTML code:

<div class="box">第一个div元素</div>
<div class="box">第二个div元素</div>
<div>第三个div元素</div>
<button>筛选box类元素</button>

JavaScript code:

$("button").click(function(){
  var result = $("div").where(".box");
  result.css("background-color", "yellow");
});

After clicking the button, the div element of the .box class will be The background color is set to yellow. Through the where() selector, we filter out elements with the .box class and modify their styles.

3. Comprehensive example

The following is a comprehensive example that uses the is() and where() selectors in combination to realize the selection and filtering operations of specific elements:

HTML code:

<div class="container">
  <div class="box">
    <p class="text">文本1</p>
    <p class="text">文本2</p>
  </div>
  <div class="box">
    <p class="text">文本3</p>
    <p class="text">文本4</p>
  </div>
</div>
<button>判断是否包含.text元素</button>

JavaScript code:

$("button").click(function(){
  var hasTextElement = $(".container").is(":has(.text)");
  if(hasTextElement){
    var result = $(".container").where(".box");
    result.removeClass("box");
  }
});

When the button is clicked, if the container element contains a .text element, all .box class elements will be removed from the box class. The is() selector is used here to determine whether the container element contains text elements. If it does, the where() selector is used to filter out the .box class elements for modification.

Through this example, we can see the power of the is() and where() selectors. They can help us accurately find the elements we need and perform corresponding operations among complex selection and filtering conditions.

Conclusion

This article introduces the use of is() and where() selectors, and demonstrates their functions and effects through code examples. Mastering these two selectors allows us to more flexibly operate elements and achieve complex effects in front-end development. I hope this article can help everyone advance in front-end programming.

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