To configure ReSharper to recognize ECMAScript 6 (also known as ECMAScript 2015) features, follow these steps:
Open ReSharper Options:
In Visual Studio, navigate to ReSharper in the top menu.
Select Options from the dropdown to open the ReSharper options window.
Navigate to JavaScript Inspections:
In the options window, expand the Code Editing section in the left-hand pane.
Click on JavaScript, then select Inspections.
Set ECMAScript Language Level:
Within the Inspections settings, locate the ECMAScript language level dropdown.
Select ECMAScript 2015 (equivalent to ECMAScript 6) from the dropdown menu.
Apply and Save:
Click Apply to save the changes.
Click OK to close the options window.