vue nextTick
()is a method for executing a delayed callback after the next DOM update loop ends. Its implementation principle is to use the browser's asynchronous task queue mechanism,tickThe callback function is placed in the queue and waited for execution. In implementation,nextTickThe method will select different underlying implementations based on the current environment. In modern browsers, it usesMutationObserverandPromiseAsynchronous task scheduling is implemented in old browsers,setTimeoutTo simulate asynchronous tasks.
The implementation principle of () is mainly to push the callback function into a queue and execute all callback functions in this queue in the next event loop cycle (MacroTask). Specifically, when the user uses () to execute the callback function, the following steps will be processed:
- First, the callback function will be pushed into a queue. This queue is called the "Async Queue", which is a container used to collect all asynchronous tasks that need to be performed during the same event loop cycle.
- Next, it will determine whether there is currently a microtask queue. If present, merge the asynchronous update queue into the microtask queue; otherwise, create a new microtask queue and add the asynchronous update queue to it.
- Next, the current execution context is captured and saved. This context contains information such as component instances, data changes, etc. of the currently executing the () method.
- Finally, a microtask is added to the microtask queue. The purpose of this microtask is to execute all callback functions in the asynchronous update queue during the next event loop cycle and restore the context before execution, ensuring that the callback functions can correctly access the relevant data.
The following is a simple example code that demonstrates the usage and implementation principle of ():
// Define a Vue instancevar vm = new Vue({
el: '#app',
data: {
message: 'Hello, world!',
},
});
// Execute the callback function after data is updated = 'Hello, !';
(function () {
('DOM updated!');
});
// Output: 'DOM updated!'
In this example, we first define a Vue instance and bind the message attribute to the page through data binding. Then, we trigger the view update by modifying the value of the message property, and add a callback function to the () method to check whether the DOM has been updated.
When we run this code, we will follow the above steps and execute the callback function in the next event loop cycle. Therefore, we can see the output in the console.
In general, () provides a very convenient way to deal with DOM updated callback functions, which can help us avoid common problems such as the delay problems that may be encountered when getting the position or size of the DOM element. At the same time, its implementation also provides us with an idea, that is, to use the event loop mechanism to manage asynchronous tasks and reasonably allocate different types of tasks to improve the performance and stability of the application.
The difference from nextTick of node
andAlthough the names are similar, their functions and uses are different.
It is a method provided, mainly used to perform certain operations after DOM updates, such as obtaining the updated DOM node after updating data. It takes advantage of the browser's asynchronous rendering mechanism to defer execution of the callback function until the next DOM update cycle.
is a method provided, mainly used to perform some operations at the end of the current event loop and before the next event loop. It allows you to execute the callback function immediately after all I/O operations in the current event loop are completed without having to wait for the next event loop.
therefore,andAlthough the names are similar, their functions and usage scenarios are different and cannot be replaced by each other.
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