Best Practices for Checking Empty Objects in Angular Templates Using *ngIf

Problem Background and Common Misconceptions

In Angular development, it's common to decide whether to render an element based on whether an object is empty. Many developers attempt to use expressions like *ngIf="previous_info != {}", but this is actually a common misconception. The issue is that every occurrence of {} in the template creates a new empty object instance, and in JavaScript, != comparisons between different object instances always return false, even if their contents are identical.

JSON Pipe Solution

The most effective solution leverages Angular's JSON pipe to convert objects to strings for comparison. The JSON pipe serializes any JavaScript object into a JSON string, allowing us to accurately determine if an object is empty through string comparison.

<div class="comeBack_up" *ngIf="(previous_info | json) != ({} | json)">
  <a [routerLink]="['Inside_group_page',{'name':previous_info.path | dotTodash }]">
    {{ previous_info.title }}
  </a>
</div>

Or using a more concise version:

<div class="comeBack_up" *ngIf="(previous_info | json) != '{}'">
  <a [routerLink]="['Inside_group_page',{'name':previous_info.path | dotTodash }]">
    {{ previous_info.title }}
  </a>
</div>

Technical Principle Analysis

The effectiveness of this method is based on several key points: First, the JSON pipe converts objects into standardized JSON string representations. For empty objects {}, the converted result is always the string '{}'. Second, string comparisons in JavaScript are value-based rather than reference-based, thus accurately reflecting object content equivalence.

It's worth noting that this method is particularly suitable for pure empty object checks. When needing to handle null, undefined, and other cases simultaneously, consider combining it with safe navigation operators or other validation mechanisms.

Alternative Solution Comparison

Besides the JSON pipe method, the development community has proposed several other solutions:

KeyValue Pipe Solution: Using *ngIf="(previous_info | keyvalue)?.length" can handle various scenarios including null, undefined, and empty objects. The KeyValue pipe converts objects into key-value pair arrays, then checks if the array length is truthy.

Custom Function Solution: Define an isEmptyObject method in the component:

isEmptyObject(obj) {
  return (obj && (Object.keys(obj).length === 0));
}

Then use it in the template: *ngIf="isEmptyObject(previous_info)". This approach offers maximum flexibility but requires maintaining additional business logic in the component.

Performance and Applicable Scenarios

The JSON pipe method generally offers the best performance in most cases, as it leverages Angular's built-in optimization mechanisms. For simple empty object checks, this is the recommended首选方案. The KeyValue pipe solution may be more advantageous when dealing with complex object structures, while the custom function solution is suitable for scenarios requiring complex validation logic.

In actual development, the choice of solution should be based on specific requirements: if only checking whether an object is empty, the JSON pipe is the most concise and effective choice; if needing to handle edge cases or perform more complex validations, other solutions can be considered.

Best Practice Recommendations

Based on years of Angular development experience, we recommend: when checking for empty objects in templates, prioritize using the JSON pipe method. This approach not only results in concise code but also offers excellent performance, meeting most practical development needs. Additionally, we recommend establishing unified code standards within teams to ensure all developers use consistent empty object checking patterns.

For complex scenarios requiring handling of null and undefined, consider combining with safe navigation operators ?., for example: *ngIf="(previous_info | json) !== '{}' && previous_info != null". This combination provides more comprehensive null value protection.