I think your example should instead be: someFunction.toString().charAt(10) == 'a' so you're getting the function's string representation, not its return v

I think your example should instead be: someFunction.toString().charAt(10) == 'a' so you're getting the function's string representation, not its return value Also I've never even considered that minifiers can break your code. To be safe it seems you either need to run minification during test & dev or setup some linting to ban features that could break during minification.