How to fix Angular 9 @ViewChild Expected 2 arguments, but got 1: An argument for 'opts' was not provided.

Problem:

You are trying to compile your Angular 9.x application, but you see an error message like

app/my-component/my-component.component.ts:24:4 - error TS2554: Expected 2 arguments, but got 1.

24   @ViewChild(MyOtherComponent) myOtherComponent: MyOtherComponent;
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

  ../node_modules/@angular/core/core.d.ts:7888:47
    7888     (selector: Type<any> | Function | string, opts: {
                                                       ~~~~~~~
    7889         read?: any;
         ~~~~~~~~~~~~~~~~~~~
    7890         static: boolean;
         ~~~~~~~~~~~~~~~~~~~~~~~~
    7891     }): any;
         ~~~~~
    An argument for 'opts' was not provided.

Solution

Find this line in your code at the location specified in the error message:

@ViewChild(MyOtherComponent) myOtherComponent: MyOtherComponent;

and add

{static: false}

as second argument to the @ViewChild() declaration:

@ViewChild(MyOtherComponent, {static: false}) myOtherComponent: MyOtherComponent;

In most cases, you want to use static: false. See this post on StackOverflow for details on when to use static: true as opposed to static: false.