What is a Mutation Observer?
A MutationObserver is a JavaScript object that acts as an observer to changes in the DOM tree. It’s a newer feature in JavaScript that allows us to watch for changes to the DOM and perform an action based on the detected change. In this blog, we’ll look at how to create a mutation observer and use it to detect changes to the DOM.
Overview of Mutation Observers
A MutationObserver is a JavaScript interface that can detect changes to the DOM and allow us to take certain actions based on these changes. The MutationObserver takes a callback function as an argument that is invoked when a mutation is detected. The callback function takes two arguments, an array of mutation records and a reference to the MutationObserver instance. The mutation records contain information about the mutation, such as the type of mutation, the target node and the added and removed nodes. From the MutationObserver instance, you can retrieve the observer’s options and shut it down.
Example of Using a Mutation Observer
Let’s look at an example of creating a MutationObserver and using it to detect changes to the DOM. We’ll create a mutation observer using the code below:
var observer = new MutationObserver(function(mutations) {
// Perform an action based on the mutation
});
The first argument to the MutationObserver is a callback function that is invoked when a mutation is detected. This callback function takes two arguments, an array of mutation records and a reference to the MutationObserver instance. We can use the mutation records and MutationObserver instance to react to the mutation.
Let’s look at a few more specifics about creating a MutationObserver.
Creating a MutationObserver
When creating a MutationObserver, you need to specify the target node and the mutation options. The target node is the DOM node that will be monitored for mutations. The mutation options is an object specifying the types of mutations that should be monitored. The options are:
- Attribute: Monitor changes to attributes.
- CharacterData: Monitor changes to character data.
- ChildList: Monitor changes to child nodes.
As an example, we can create a mutation observer monitor changes to the target node’s attributes with the following code:
var observer = new MutationObserver(function(mutations) {
// Perform an action based on the mutation
}, {
attributes: true
});
The mutation observer will now be triggered any time a mutation is detected on the target node’s attributes.
Accessing Mutations
The mutation records array passed to the MutationObserver callback function contains information about the mutation. The records contain information about the type of mutation, the target node and added/removed nodes and attributes. This can be accessed from the MutationRecord object.
For example, let’s say we want to log the target node and the added nodes when a mutation is detected. We can access this information from the MutationRecord like so:
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(mutation) {
console.log(mutation.target, mutation.addedNodes);
});
});
The above code will log the target node and added nodes to the console when a mutation is detected.
Conclusion
In this blog post, we looked at MutationObserver and how it can be used to detect changes to the DOM. We saw how to create a MutationObserver and how to access mutation records from the MutationObserver’s callback function. With this knowledge, you should now be able to use MutationObserver to detect changes to the DOM and take appropriate actions.
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