Angular Interview Practice

How does *ngIf differ from *ngFor?

1. *ngIf creates a template for collections

2. *ngFor conditionally adds an element

3. *ngIf modifies the DOM structure based on boolean expression

4. *ngFor changes styles of elements

The correct answer is: *ngIf modifies the DOM structure based on boolean expression

The distinction between *ngIf and *ngFor is fundamental to understanding how Angular manipulates the DOM. When using *ngIf, it literally evaluates a boolean expression and conditionally includes or excludes an element from the DOM based on the result of that expression. If the expression evaluates to true, the associated template is rendered; if false, the template is removed from the DOM entirely. This means that *ngIf can be used to show or hide elements dynamically based on user interactions or application state. In contrast, *ngFor is specifically designed for iterating over collections, creating a new instance of the template for each item in that collection. Therefore, it does not deal with conditional display based on boolean logic but rather focuses on rendering lists. This key function of *ngIf to modify the DOM structure based on a condition is what makes option C the correct and relevant choice for this question. Understanding this difference is crucial for developers as it directly impacts how they control the visibility of components in their applications.