I'm using angularJS 5 and boostrap 4. Then I added Bootstrap-select v1.13.0-beta to app from here. Bootstrap-select v1.13.0
I have also made sure that jQuery is being loaded before Boostrap-select.js
<form [formGroup]="userRegform" novalidate>
<fieldset class="form-group">
<select class="form-control selectpicker" name="testtype" formControlName="testtype" data-live-search="true">
<option>a</option>
<option>b</option>
<option>c</option>
</select>
</fieldset>
<button type="submit">Next</button>
</form>
If you intend to use bootstrap-select in Angular for anything more than a very basic use case, I would highly recommend you take steps to wrap it in an angular directive.
While it is not using the latest v1.13.0-beta, I have an example project demonstrating use of bootstrap-select within angular using bootstrap4: https://github.com/braheem/angular-bootstrap-select
If you are adamant about using v1.13.0-beta of bootstrap-select, you can try a similar approach as done in the linked project, but swap out the version of bootstrap-select with the beta version you are using.