Detailed explanation of how Vue efficiently updates the UI

Virtual DOM and Diff algorithm: How to efficiently update the UI with Vue?

In modern front-end development, it is known for its efficient and responsive data binding and view update mechanism. And one of the core technologies of all this is the virtual DOM (Virtual Document Object Model) and the Diff algorithm. This article will introduce in detail the concept of virtual DOM, how Diff algorithm works, and how Vue can use these technologies to efficiently update the UI.

What is a virtual DOM?

definition

Virtual DOMIt is a lightweight JavaScript object used to represent the state of the DOM tree. It mimics the structure and interface of a real DOM, but does not interact directly with the browser's underlying layer. By separating view logic from actual DOM operations, developers can manage UI updates more efficiently.

Advantages of virtual DOM

1. Reduce DOM operations: Virtual DOM allows efficient node comparison and update in memory, rather than directly modifying the DOM every time.
2. Batch Optimization: Multiple state changes can be merged into one-time updates in memory.
3. Easy to debug and test: Since virtual DOM is a pure JavaScript object, debugging and unit testing are more convenient.

Diff algorithm: How to efficiently calculate UI differences

definition

**Diff Algorithm** is an algorithm used to compare two tree structures and find out the differences between them. In Vue, the Diff algorithm is used to compare the old virtual DOM tree with the new virtual DOM tree, generating the smallest update operation (called "patch"), thus minimizing the actual DOM operation.

Core idea

1. Only compare the changing parts: By comparing the tree structure layer by layer, find the specific nodes that need to be updated.
2. Reuse the same part: For the unchanged parts, directly reuse the old DOM nodes to avoid repeated creation and destruction.
3. Minimize operation: Generate update instructions only for changed parts.

Steps of the Diff algorithm

1. Compare the root node：
   • If the root node type is different (for example, a node is<div>, the other one is<span>), directly replace the entire node.
2. Compare child nodes：
   • For child nodes, compare one by one in order. If a child node at a certain location changes, an insert, delete, or update operation is generated.
3. Process text content：
   • If the node type is text (such as a normal string), directly compare the text content and update it.

Sample code

Here is a simple Diff algorithm implementation:

function diffNodes(oldNode, newNode) {
  if ( !== ) {
    return { type: 'replace', node: newNode };
  }

  // Process text nodes  if ( === undefined &&  === undefined) {
    if ( !== ) {
      return { type: 'update', value:  };
    }
    return null;
  }

  // Compare child nodes  const patches = [];
  for (let i = 0; i < (, ); i++) {
    const oldChild = i <  ? [i] : null;
    const newChild = i <  ? [i] : null;

    const patch = diffNodes(oldChild, newChild);
    if (patch) {
      (patch);
    }
  }

  return  > 0 ? { type: 'children', patches } : null;
}

Virtual DOM and Diff algorithm in Vue

Implementation of virtual DOM

Vue converts view logic into a virtual DOM tree in a componentized way. Each component corresponds to a virtual node (vnode), containing the following properties:

• type: Node type (e.g.'text'、'element'）。
• props: Attributes, including data binding and event processing.
• children: child node array.

Optimization of Diff algorithm

Vue has performed multiple optimizations based on the Diff algorithm:

1. Index-based updates：
   • Use array indexes to determine where to insert, delete, or move, rather than completely rerendering the entire list.
2. Stable Mapping (Keyed Children)：
   • By a unique key value (keyProperties) to track and multiplex dynamically generated child nodes to avoid unnecessary reconstruction.

Example: List update in Vue

Here is a simple Vue component that shows how to efficiently update the list UI:

<template>
  <div>
    <ul>
      <!-- usev-forDirective rendering list -->
      <li v-for="item in list" :key="">{{  }}</li>
    </ul>
  </div>
</template>

<script>
export default {
  data() {
    return {
      list: [
        { id: 1, value: 'Item 1' },
        { id: 2, value: 'Item 2' }
      ]
    };
  },
};
</script>

In Vue, the above code is compiled into a virtual DOM tree and the UI is updated efficiently through the Diff algorithm. For example, whenlistWhen an array changes (such as adding or removing items), Vue will automatically calculate the parts that need to be updated and apply them to the real DOM.

Performance comparison: Vue's virtual DOM operation vs Vue's

Disadvantages of traditional methods

• Frequently re-rendered: Directly modifying the DOM will cause the browser to frequently re-render the page, especially in scenarios with large amounts of data.
• Performance bottleneck:For complex UIs, DOM operations will become a performance bottleneck.

Advantages of Vue

Through virtual DOM and Diff algorithms, Vue can significantly reduce unnecessary DOM operations. For example:

• In a list update, Vue only updates the changed parts, rather than re-rendering the entire list.
• Although virtual DOM increases memory consumption, the performance improvements it usually exceed the cost of memory consumption.

Summarize

Virtual DOM and Diff algorithms are the core technologies for Vue to implement efficient UI updates. By separating view logic from actual DOM operations and leveraging the principle of minimizing update operations, Vue can provide a simple and easy-to-use development experience while ensuring high performance.

This is the end of this article about the detailed explanation of how Vue is efficiently updated UI. For more related content on Vue update UI, please search for my previous articles or continue browsing the related articles below. I hope everyone will support me in the future!