Introduction

Ember.js follows a convention-over-configuration approach, but improper state management, excessive data re-fetching, and inefficient template bindings can degrade performance. Common pitfalls include memory leaks from lingering observers, redundant computed property recalculations, excessive dependency tracking in tracked properties, improper component teardown in `willDestroy`, and inefficient Glimmer rendering. These issues become particularly problematic in large-scale Ember applications where re-rendering inefficiencies directly impact responsiveness. This article explores common causes of performance degradation in Ember.js, debugging techniques, and best practices for optimizing data handling and component lifecycle management.

Common Causes of Performance Bottlenecks and Memory Leaks

1. Memory Leaks Due to Unremoved Event Listeners and Observers

Failing to clean up event listeners and observers can cause memory leaks.

Problematic Scenario

import Component from "@glimmer/component";
import { action } from "@ember/object";

export default class ExampleComponent extends Component {
  constructor() {
    super(...arguments);
    window.addEventListener("resize", this.handleResize);
  }

  @action
  handleResize() {
    console.log("Window resized");
  }
}

This component does not remove the event listener, leading to a memory leak when unmounted.

Solution: Remove Event Listeners in `willDestroy`

import Component from "@glimmer/component";
import { action } from "@ember/object";
import { on } from "@ember/modifier";

export default class ExampleComponent extends Component {
  constructor() {
    super(...arguments);
    this.handleResize = this.handleResize.bind(this);
    window.addEventListener("resize", this.handleResize);
  }

  willDestroy() {
    super.willDestroy(...arguments);
    window.removeEventListener("resize", this.handleResize);
  }

  @action
  handleResize() {
    console.log("Window resized");
  }
}

Cleaning up event listeners prevents memory leaks.

2. Excessive Computed Property Recalculation

Computed properties that track too many dependencies can slow down rendering.

Problematic Scenario

import { computed } from "@ember/object";

export default class ExampleComponent extends Component {
  @computed("user.name", "user.email", "user.address")
  get userInfo() {
    return `${this.user.name} - ${this.user.email} - ${this.user.address}`;
  }
}

Tracking multiple properties leads to unnecessary recomputations.

Solution: Use `@tracked` Properties for Granular Updates

import { tracked } from "@glimmer/tracking";
import { action } from "@ember/object";

export default class ExampleComponent {
  @tracked userInfo;

  @action
  updateUserInfo(user) {
    this.userInfo = `${user.name} - ${user.email}`;
  }
}

Using `@tracked` ensures updates happen only when necessary.

3. Inefficient Data Fetching Causing Unnecessary Re-Renders

Fetching data inefficiently inside component lifecycle hooks can cause excessive re-fetching.

Problematic Scenario

import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";
import { task } from "ember-concurrency";

export default class UserListComponent extends Component {
  @tracked users = [];

  constructor() {
    super(...arguments);
    this.loadUsers();
  }

  async loadUsers() {
    let response = await fetch("/api/users");
    this.users = await response.json();
  }
}

This approach triggers data fetching every time the component is instantiated.

Solution: Use `ember-concurrency` to Manage Data Fetching Efficiently

import Component from "@glimmer/component";
import { tracked } from "@glimmer/tracking";
import { task } from "ember-concurrency";

export default class UserListComponent extends Component {
  @tracked users = [];

  @task
  *loadUsers() {
    let response = yield fetch("/api/users");
    this.users = yield response.json();
  }

  constructor() {
    super(...arguments);
    this.loadUsers.perform();
  }
}

Using `ember-concurrency` ensures data is fetched only when needed and avoids race conditions.

4. Unoptimized Template Bindings Increasing Reconciliation Costs

Using dynamic helpers inside templates can cause excessive re-renders.

Problematic Scenario

{{#each this.users as |user|}}
  {{user.firstName}} {{user.lastName}} is {{if user.active "Active" "Inactive"}}
{{/each}}

Each render recalculates the `if` statement for every user.

Solution: Precompute Derived Data

{{#each this.processedUsers as |user|}}
  {{user.fullName}} is {{user.status}}
{{/each}}

Processing derived data in the component prevents unnecessary recalculations.

5. Excessive Dependency Tracking in Tracked Properties

Tracking complex objects without proper reference management can slow down updates.

Problematic Scenario

import { tracked } from "@glimmer/tracking";

export default class UserComponent {
  @tracked user = { name: "John", age: 30 };

  updateUserAge() {
    this.user.age += 1; // Won't trigger reactivity
  }
}

Updating nested properties does not trigger reactivity.

Solution: Use Shallow Updates with New Object References

updateUserAge() {
  this.user = { ...this.user, age: this.user.age + 1 };
}

Using a new object reference ensures updates trigger reactivity.

Best Practices for Optimizing Ember.js Performance

1. Clean Up Event Listeners and Observers

Prevent memory leaks by removing listeners in `willDestroy`.

Example:

window.removeEventListener("resize", this.handleResize);

2. Optimize Computed Properties

Use `@tracked` properties for more efficient updates.

Example:

@tracked userInfo;

3. Use `ember-concurrency` for Efficient Data Fetching

Prevent redundant API calls.

Example:

this.loadUsers.perform();

4. Optimize Template Bindings

Precompute derived data in components.

Example:

this.processedUsers = this.users.map(user => {...})

5. Use Immutable Updates for Tracked Properties

Ensure updates trigger reactivity.

Example:

this.user = { ...this.user, age: this.user.age + 1 };

Conclusion

Performance bottlenecks and memory leaks in Ember.js often result from unoptimized event handling, inefficient data fetching, excessive dependency tracking, and improper component lifecycle management. By implementing cleanup functions, optimizing computed properties, using `ember-concurrency`, and ensuring immutable state updates, developers can significantly improve Ember application performance.