What does Angular 2 use to update the DOM. Is it Shadow DOM or Virtual DOM ? Was there any such concept in Angular 1?
Shadow DOM is now directly supported.
Angular2 doesn't use shadow DOM (default) nor virtual DOM.
encapsulation: ViewEncapsulation.Emulated (default) there is no shadow DOM because style encapsulation is only emulated.
encapsulation: ViewEncapsulation.Native enables shadow DOM on browsers that support it natively or it's again emulated when the webcomponents polyfill is loaded.
Shadow DOM is also not targeting performance as virtual DOM is, but style encapsulation.
Angular2 doesn't use virtual DOM at all.
Angular2 has change detection that detects changes to the model and only updates the parts of the DOM that need to be changed according to the model changes.
For more details see also Is Shadow DOM fast like Virtual DOM in React.js?
React and Vue are using Virtual DOM and Angular use direct DOM rendering system.
It's the same thing that Angular did with version 1.x, but it is optimized and there is a surprise for you :)
Angular 2 and the version came after doesn't use Virtual DOM instead it uses change detection mechanism to detect any change and act upon it while React and Vue uses Virtual DOM to compare with the Real DOM to detect any change occurred.
On the other hand in some way Angular does uses Shadow DOM in encapsulation to keep the markup structure, style, and behaviour hidden and separate from other code or components on the page so that different parts do not clash. you can learn more about encapsulation here.
And the last part there is no such concept of Virtual DOM and Shadow DOM used in Angular 1 or AngularJS.