Angular's Incremental DOM vs. Virtual DOM Explained

Anton Ioffe - November 28th 2023 - 10 minutes read

As we navigate the intricate landscape of modern web development, Angular's embrace of Incremental DOM has sparked a dialogue about its distinct approach to managing UI updates compared to the widespread use of Virtual DOM. In this article, we'll dissect the inner workings of Angular Ivy's Incremental DOM, juxtapose its fine-grained rendering process with the abstraction layers of Virtual DOM, and distill concrete practices for leveraging its potential within your Angular projects. Through detailed technical insights and comparative analysis, we will explore the tangible implications on performance, memory management, and the developer experience, equipping you with a nuanced understanding to make informed decisions on which paradigm aligns with the needs of your cutting-edge applications. Prepare to unravel the nuances behind these transformative DOM manipulation strategies and chart a path through the complexities of modern front-end development.

Section 1: Angular Ivy and the Emergence of Incremental DOM

Angular Ivy, with its transition to Incremental DOM, marks a significant shift in the landscape of modern web development frameworks. Incremental DOM's distinction lies in its unique approach to updating the DOM directly in-place, marking a departure from the traditional virtual tree-based updates. This model reduces the memory footprint and mitigates garbage collection bottlenecks, favoring in-situ modifications over creating and comparing comprehensive virtual representations of the DOM. Such an approach embodies the principle that efficiency in memory utilization can be key to performance optimization.

With the launch of Angular Ivy, design decisions resonate with the framework's heritage of embracing HTML and templates. Angular champions a declarative paradigm, which aligns with the Incremental DOM's instruction-based update strategy. Rather than resorting to virtual tree diffing, updates occur directly as instructions influenced by template expressions, aligning with the component-centric nature of Angular. This integration results in a predictable performance, an attribute crucial in devices with limited resources, like mobile handsets.

Angular Ivy's incorporation of tree shaking stands as testament to the performance-centric ethos of Incremental DOM; this technique eliminates dead code from the application build. The symbiosis between Angular and Incremental DOM facilitates the generation of concise component-specific instructions, enabling Angular to shed unnecessary code with ease. This leads to lean, efficient builds—a more complex task in virtual DOM-based frameworks, due to their typically larger runtime libraries.

The symbiosis of Angular Ivy and Incremental DOM represents a strategic and forward-thinking move for Angular's rendering prowess. This synergy not only elevates rendering efficiency but also capitalizes on Angular's strengths. The streamlined processing model inherent in Incremental DOM empowers Angular to uphold its HTML-centric philosophy, thereby solidifying its status as an efficient, powerful tool for creating sophisticated applications without sacrificing performance.

Angular's commitment to Incremental DOM stems from a design ethos that emphasizes direct, fine-grained DOM manipulation, eschewing the reliance on virtual DOM employed by other frameworks. With Incremental DOM, Angular advocates a considered approach to DOM updates, providing granular control over each modification. Such an approach reflects a conscious deviation from the prevalent trend of utilizing virtual representations, fostering a mindful balance between the actual DOM and the updates it undergoes, underpinning Angular's resolve in pushing the envelope of web development.

Section 2: The Virtual DOM Paradigm

The Virtual DOM paradigm operates on the premise of optimizing rendering performance by minimizing direct DOM manipulations. The process unfolds in three key steps: initially, a virtual representation of the user interface is established in memory, then modifications between the current virtual state and the last are identified through a diffing algorithm, and finally, the calculated changes—expressed as patches—are applied to the actual DOM, circumventing the need for complete page re-renders.

In the virtual tree creation phase, developers construct a structural model that resembles the DOM's hierarchy of elements. This model itself, while fundamental to the Virtual DOM approach, incurs a substantial memory overhead. For immense applications that handle complex data and state-driven interfaces, building and holding each new virtual tree in memory can increase both memory usage and the computational load of each update cycle.

The diffing process employs an algorithm to ascertain precisely what differs between instances of virtual trees. These derived changes yield a set of operations that facilitate transitioning from the old state to the new one. However, the efficiency of this process is not without potential drawbacks. Applications with multiple dynamic states and components can strain performance, as each requires continual assessment and diff computation, potentially impacting user experience through decreased responsiveness.

Patching occurs when the changes identified during diffing are strategically transposed onto the actual DOM. This is designed to streamline rendering updates, but the intricacy involved in handling a number of changes simultaneously can lead to computationally heavy operations. Interactive applications that undergo frequent state updates stand risk high performance costs during this phase.

Below is a conceptual code example that reflects the Virtual DOM's methods for managing updates via a diffing process:

function diffAttributes(oldAttrs, newAttrs) {
    const patches = [];
    Object.keys(oldAttrs).filter(key => !(key in newAttrs))
        .forEach(key => patches.push({ type: 'REMOVE_ATTRIBUTE', key }));
    Object.entries(newAttrs).filter(([key, value]) => oldAttrs[key] !== value)
        .forEach(([key, value]) => patches.push({ type: 'SET_ATTRIBUTE', key, value }));
    return patches;

function diffChildren(oldChildren, newChildren) {
    const patches = [];
    const childPatches = [];
    oldChildren.forEach((oldChild, i) => {
        childPatches.push(diff(oldChild, newChildren[i]));
    const additionalPatches = newChildren.slice(oldChildren.length)
        .map(newChild => ({ type: 'APPEND', newChild }));
    return patches.concat(childPatches).concat(additionalPatches);

function diff(oldNode, newNode) {
    if (newNode === undefined) {
        return [{ type: 'REMOVE', oldNode }];
    if (typeof oldNode === 'string' || typeof newNode === 'string') {
        if (oldNode !== newNode) {
            return [{ type: 'TEXT', newText: newNode }];
        } else {
            return [];
    if (oldNode.tagName !== newNode.tagName) {
        return [{ type: 'REPLACE', newNode }];
    const attributePatches = diffAttributes(oldNode.attributes, newNode.attributes);
    const childrenPatches = diffChildren(oldNode.children, newNode.children);
    return [...attributePatches, ...childrenPatches];

Patches may include a variety of changes like 'SET_ATTRIBUTE' for updating an attribute, or 'APPEND' for adding a child node.

Through this example, we gain insights into the deliberate minutiae of the Virtual DOM's diffing and patching framework. The code underscores the delicate balance required to handle the simultaneous update operations, which is indicative of the broader scope of how the Virtual DOM strives to handle dynamic lists and state transitions effectively.

In the sphere of modern web development, the need to weigh performance versus memory overhead cannot be overstated. The implementation of such rendering optimizations must be carefully considered to ensure applications maintain fluidity and responsiveness.

Section 3: Incremental DOM Under the Hood

Incremental DOM strategically compiles each component into explicit instructions, bypassing the virtualized layers found in other frameworks. These instructions are directly committed to the live DOM. Incremental DOM capitalizes on actual DOM nodes as benchmarks for incoming updates, thereby eliminating the overhead associated with managing an extensive virtual DOM tree and easing the pressure on garbage collection.

During component initialization within Incremental DOM, a template function is generated that breaks down into a succinct set of operations like elementOpen, text, and elementClose. Upon data changes that impact the component's display, Incremental DOM recalibrates and carries out only the specific instructions affecting the altered segments of the DOM.

function render(title) {
const initialTitle = 'Hello, Incremental DOM!';
render(initialTitle); // Executes the full rendering
// When the title is updated...
const updatedTitle = 'Goodbye, Incremental DOM!';
render(updatedTitle); // Only updates the text node

Through this method, substantial performance improvements are especially notable in environments with constrained memory resources. This is because Incremental DOM performs modifications directly on the DOM nodes, striving to lower the resource burden associated with the construction of nodes and their subsequent cleanup. The framework targets the exact changes needed, avoiding the overhead of complete virtual DOM tree re-assembly and delta calculations.

A key aspect of Incremental DOM is its dedication to optimizing memory use. It utilizes an instruction set that activates upon data alteration to reduce memory consumption. This is vital for dynamic web applications demanding peak performance, as it affects not only runtime memory but also the necessity for an always-present virtual analog.

While the potential for performance and memory efficiency is a critical advantage, developers must be vigilant in maintaining code readability and managing complexity. The Instruction-based methodology demands familiarity with Incremental DOM's processes to prevent unnecessary code bloat. The goal is to craft instruction sets that embody peak performance without sacrificing the maintainability and navigability of the code.

Section 4: Cutting Through Complexity: Best Practices in Incremental DOM

When integrating Incremental DOM into your Angular projects, focusing on a modular design and maximizing reusability is paramount. By dividing your application into self-contained modules, each with a clear responsibility, you can greatly ease the process of maintaining and updating your codebase. Reusable components should be designed to be as stateless as possible, receiving data through inputs and emitting events through outputs. This design pattern not only enhances the predictability of your components but also renders them more testable and maintainable. Remember to keep your components focused; a component should address a single concern to simplify both the development and the optimization process later on.

In the realm of Incremental DOM, code organization is a critical factor. Strive to segregate your logic from your templates. This separation encourages better maintenance and testing practices, as it becomes straightforward to locate and address issues in either logic or representation. Additionally, this clarity facilitates easier reusability, as the logical parts of your application can be abstracted and reused without dragging along template code that may not be applicable in every use case.

To avoid common pitfalls, one should adhere to disciplined change detection strategies. Do not unnecessarily trigger change detections or updates, as excessive updates can lead to performance bottlenecks, especially in memory-constrained environments. Use lifecycle hooks judiciously and only when you need to react to changes. Also, take advantage of Angular's OnPush change detection strategy to minimize unnecessary view updates, leveraging the framework's optimization capabilities to your advantage.

Advanced techniques to optimize performance include leveraging lazy loading for modules and components, which helps in reducing the initial load time and memory consumption. Additionally, consider the use of trackBy functions in ngFor directives to minimize DOM manipulations by instructing Angular on how to identify items uniquely within a collection. This practice leads to significant performance improvements, especially in scenarios with frequent updates of large lists.

Lastly, it is crucial to perform regular performance audits on your Angular application to detect any potential inefficiencies introduced by misuse or misunderstanding of the Incremental DOM. Profiling your application can give insights into bottlenecks and allow you to undertake targeted optimizations. However, be wary of premature optimization; always measure and evaluate the impact before dedicating time to optimize certain parts of your application. By following these best practices, you can harness the full potential of Incremental DOM while maintaining a clean, maintainable, and performance-oriented Angular codebase.

Section 5: Comparing Performance, Memory, and Developer Experience

When comparing Incremental DOM and Virtual DOM, it's important to dive into the key metrics of performance, memory usage, and developer experience. Performance-wise, Virtual DOM's reconciliation strategy can be a double-edged sword. The creation of a new virtual DOM tree for detecting changes introduces overhead but can result in efficient batch updates to the real DOM. This makes quick work of complex UI changes but can be overkill for minor tweaks, resulting in unnecessary computational work. On the flip side, Incremental DOM eschews the virtual DOM model, applying changes in place and thus minimizing resource computation at the expense of potentially slower DOM updates because it must traverse the DOM tree to apply changes.

Memory usage patterns are another battleground. Virtual DOM typically consumes more memory due to its requirement for a copy of the DOM in memory which needs to be updated on each render cycle. In contrast, Incremental DOM's in-place update philosophy shines here, using a significantly smaller memory footprint—which is paramount for devices with limited resources. Incremental DOM excels in scenarios where memory is at a premium, such as on mobile browsers, where it conservatively uses memory only for changes detected in the DOM.

For developers, experience with each DOM approach varies considerably. The Virtual DOM is known for its developer-friendly abstraction; React's JSX, for example, allows developers to work with UI in a declarative and readable manner. Moreover, the framework takes care of diffing and patching, which streamlines the development process. However, the underlying complexity can make debugging challenging. With Incremental DOM, developers retain fine-grained control with a more explicit, instruction-based approach—this can provide clarity on exactly how and when DOM modifications occur but also demands deeper knowledge and experience to avoid pitfalls.

Real-world applications need careful consideration of these trade-offs. For instance, when dealing with high-performance or real-time applications (like games or interactive graphics), where every millisecond counts, developers might favor Virtual DOM for its faster reconciliation in scenarios with substantial UI changes. Conversely, applications that are lighter on dynamic UI updates, particularly those targeting mobile devices with lower memory capacities, would benefit from the trimmed resource requirements of Incremental DOM.

Considering these factors prompts reflection on the suitability of each approach given the specific needs of a project. Are relatively frequent but minor updates more common than less frequent but larger updates in your application? Does your user base primarily engage via mobile devices? How significant is the learning curve for your development team when picking a DOM strategy? Evaluating both strategies against these real-world concerns enables developers to make informed decisions based on the app's requirements, leading to more performant and resource-efficient applications.


In this article, we explored the differences between Angular's Incremental DOM and the widespread use of Virtual DOM in modern web development. We discussed how Incremental DOM updates the DOM directly in-place, reducing memory usage and improving performance. We also highlighted the advantages and drawbacks of the Virtual DOM paradigm. The key takeaway is that developers need to carefully consider the trade-offs between performance, memory usage, and developer experience when choosing between Incremental DOM and Virtual DOM for their projects. As a challenging task, readers can analyze their own applications and evaluate which DOM strategy aligns best with their specific needs and goals. They should consider factors such as the frequency and scale of UI updates, the memory resources available, and the development team's familiarity with each approach.

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