When to Use Track by?

You can use track by $index if you do not have a unique identifier. If you are using "track by" then it will avoid generating DOM elements every times for element that are already rendered. It improves the rendering performance.

What is difference between ngFor and Ng-repeat?

ng-repeat created inherited child scope for each element of collection, while *ngFor creates local variable in the that block.

What is ngRepeat?

Angular-JS ng-repeat directive is a handy tool to repeat a set of HTML code for a number of times or once per item in a collection of items. ng-repeat is mostly used on arrays and objects. ... Here “MyObjectName” is a collection that can be an object or an array and you can access each value inside it using a “keyName”.