Anil Singh | Code-sample.com

The “ track by ” expression to specify unique keys.   The “ track by ” takes a function that has two arguments: index and item. If “track by” is given, Angular tracks changes by the return value of the function. Understanding About *ngFor Mechanisms:- By default, when you use * ngFor without “track by”, *ngFor tracks array of objects changing through object identity. If you are going to modify (add, update, remove) any element of * ngFor , then update the tracking algorithm by providing your object id to the “track by”function.” Why use “track by”with ngFor directive? The “ngFor” directive may perform poorly with large lists. A small change to the list like, adding a new item or removing an existing item may trigger several DOM manipulations. Syntax of ngFor Angular: < tr   *ngFor = "let user of users; let i = index" >      < td > {{user.name}} </ td >    ...