Core Concepts Behind Element UI

Reactive Data Flow and DOM Binding

Element UI relies on Vue's reactivity system. Components like el-table, el-form, and el-dialog dynamically bind to reactive data, which must follow immutability and declarative update principles to remain in sync with the DOM.

Layout System

Grid-based components (el-row, el-col) use Flexbox. Issues with responsiveness often arise due to conflicting CSS from external libraries or incorrect slot usage.

Common Problems and Root Causes

1. el-table Not Reacting to Data Changes

When using el-table with dynamic arrays, you may encounter rows not updating even after modifying the bound array. This often happens due to non-reactive mutations:

this.tableData.push(newRow); // Works
this.tableData[2] = newData; // NOT reactive

Fix by using Vue.set:

this.$set(this.tableData, 2, newData);

2. el-dialog Not Closing Properly

If you use v-if instead of v-show to control dialog visibility, the component is destroyed and re-mounted each time, resetting its state:

<el-dialog v-if="visible" ...>

Use v-show unless you explicitly want the component destroyed:

<el-dialog v-show="visible" ...>

3. Form Validation Not Triggering

el-form-item depends on correct prop mapping and model nesting. Mismatched keys or nested objects can break validation silently.

<el-form :model="form">
  <el-form-item prop="email">
    <el-input v-model="form.user.email" /> // prop is email, but model is form.user.email
  </el-form-item>
</el-form>

Ensure the prop matches the v-model path exactly.

4. el-select Dropdown Rendering Off-Screen

This usually happens inside modals or scroll containers. Element UI uses absolute positioning for dropdowns and detaches them from the parent DOM node.

Solutions:

• Set append-to-body=false
• Apply correct z-index stacking
• Manually trigger updatePopper() after visibility change

5. Table Column Misalignment

Occurs when columns use complex scoped slots or hidden columns. Sometimes caused by DOM not being fully ready when width is calculated.

Fix:

• Use v-if sparingly on el-table-column
• Call doLayout() on el-table after data or layout changes

Diagnosing and Debugging Techniques

1. Use Vue DevTools

Inspect reactive props, component hierarchy, and emitted events. Helps verify that v-model is correctly bound and lifecycle hooks are executing.

2. Watch Console Warnings

Element UI emits console warnings when props or events are misused. Pay attention to slot misuse, deprecated props, or missing model bindings.

3. Isolate Components During Debugging

Extract problem components into a minimal reproduction in a sandbox project. Many layout or behavior issues are context-specific (CSS collisions, DOM structure).

4. Profile Rendering Bottlenecks

Use Chrome DevTools Performance tab to identify slow component re-renders, especially in tables with thousands of rows.

Fixes and Optimization Strategies

1. Avoid Deep Watchers on Large Objects

watch: {
  deepWatchedObject: {
    handler(val) { ... },
    deep: true
  }
}

Deep watchers can cause performance issues. Instead, flatten your model or use shallow comparison techniques.

2. Use Virtualized Tables for Large Datasets

Element UI does not provide virtualization out-of-the-box. Integrate libraries like vue-virtual-scroll-list to render only visible rows.

3. Minimize Component Nesting

Overusing nested custom components around Element UI widgets can cause rendering chain delays and layout thrashing.

4. Tune reactivity with computed properties

computed: {
  filteredList() {
    return this.items.filter(...);
  }
}

Use computed properties instead of methods for reactive data transformations.

Best Practices for Scalable Element UI Usage

• Use scoped slots for flexibility and layout control
• Centralize all form model definitions and validations
• Use CSS BEM naming to prevent class conflicts
• Debounce input-heavy interactions (e.g., el-input, el-select)
• Don't mix v-if and v-show unnecessarily

Conclusion

Element UI offers powerful components out of the box, but its effectiveness in large applications depends on deep understanding of Vue's reactivity and lifecycle mechanisms. Troubleshooting common issues such as non-reactive updates, layout shifts, or form validation failures requires a combination of architectural discipline and practical debugging techniques. By adhering to best practices, optimizing reactivity, and leveraging profiling tools, developers can achieve smooth and scalable front-end experiences using Element UI.

FAQs

1. Why is my el-table not updating after data change?

You likely mutated the array non-reactively. Use Vue.set or assign a new reference to the data array.

2. How do I prevent el-dialog from resetting state every time?

Use v-show instead of v-if to preserve component instance and avoid destruction/recreation.

3. Why is my dropdown going off-screen inside modals?

Set append-to-body to false and ensure container has correct overflow and z-index values.

4. How can I handle large datasets in el-table?

Integrate a virtual scroll library or paginate your data to prevent full DOM rendering of thousands of rows.

5. Is Element UI compatible with Vue 3?

No, Element UI is for Vue 2. For Vue 3, use Element Plus which is a community-supported migration of Element UI.