How to fix this warning 'var' used instead of 'let' or 'const' JsLint in phpStrom?

Open PhpStorm Settings -> Languages & Framework -> Javascript and in "JavaScript language version" dropdown select EcmaScript 5

in Settings , find Inspections tab . Then find the one denoted in picture below (which is "'var' used instead of 'let' or 'const'", and change the severity to no highlighting.

The squiggling line disappears after you apply this new setting.