How jquery monitors changes in span elements

With the development of web technology, event-driven front-end development is becoming more and more important. Among them, jquery's unparalleled observer mode provides us with a good event monitoring solution, and is becoming more and more popular among programmers.

This article will introduce a method of using jquery to monitor span element changes, allowing developers to obtain the latest value of span elements in real time, providing more possibilities for event-driven programs.

jquery's method of monitoring span element changes

Let's first take a look at jquery's event listening method: .on(). In jquery, we can use it to register event handlers.

But for the span element, it does not have a special input event like the input element. However, we can simulate input events through other events.

In this article, we will use a DOM listener named [MutationObserver](https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver) to listen for span elements The innerText property change event.

MutationObserver

MutationObserver is a new type of DOM listener supported by modern browsers. It can monitor changes in any node in the DOM and respond to these changes through callback functions.

The typical usage of MutationObserver is listed below:

// 监听某个元素以及其子元素在 DOM 树中的所有变化
var observer = new MutationObserver(callback);
observer.observe(targetElement, config);

Among them, callback is a callback function. When the target element or its sub-elements change, the callback function will be called back. targetElement is the DOM element to be monitored, and the config parameter is a configuration object that allows us to configure the properties to be monitored when the element changes.

For the example of this article, we will listen to the innerText attribute change event of the span element:

var observer = new MutationObserver(function(mutations) {
  mutations.forEach(function(mutationRecord) {
    console.log('innerText changed:', mutationRecord.target.innerText);
  });
});
observer.observe(document.getElementById('mySpan'), { characterData: true, subtree: true });

Among them, characterData: true allows us to listen Changes in the content of the target element. The subtree: true parameter allows us to monitor changes in all descendant elements of the target element.

Implementation

After having the above foundation, we can start to implement the function of jquery monitoring span element changes.

First, we need to get the span element to be monitored through jquery, and then use the native DOM object to create a MutationObserver instance.

var $span = $('span');
var observer = new MutationObserver(function(mutations) {
  mutations.forEach(function(mutationRecord) {
    console.log('innerText changed:', mutationRecord.target.innerText);
  });
});

Next, we need to convert the jquery object into a native DOM object.

var span = $span[0];

Finally, through the observe() method, we add the span element to the MutationObserver:

observer.observe(span, { characterData: true, subtree: true });

In this way, when the content of the span element changes, we You can monitor changes through MutationObserver and get the latest content in real time.

Summary

This article introduces a method of using jquery to monitor changes in span elements. It monitors the innerText attribute change events of span elements through MutationObserver, thereby achieving real-time acquisition of span elements. The purpose of the latest value.

This method can be easily applied to event-driven programs, providing developers with more possibilities.

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