ViewChild is a decorator that allows you to get a reference to a child component, directive, or element within a parent component. ElementRef, on the other hand, is a class that provides access to the underlying DOM element of a component or directive. While ElementRef can be useful in some cases, it should be used sparingly because it can have a negative impact on performance.

ViewChild is a better alternative to ElementRef because it provides a more efficient way to access child components, directives, or elements. When you use ViewChild, Angular only needs to search for the child component, directive, or element once, when the view is initialized. After that, the reference to the child is stored in memory and can be accessed quickly and efficiently. This can lead to significant performance improvements, especially in large or complex applications.

Here is an example of how to use ViewChild to get a reference to a child component:

import { Component, ViewChild } from '@angular/core';
import { ChildComponent } from './child.component';

@Component({
  selector: 'parent-component',
  template: `
    <child-component></child-component>
  `
})
export class ParentComponent {
  @ViewChild(ChildComponent) childComponent: ChildComponent;
}

In this example, we use the ViewChild decorator to get a reference to the ChildComponent. We then store the reference in a property called childComponent. This allows us to access the child component's properties and methods from the parent component.