The compiler knows what you're doing. A keyword like 'field's inside a function's braces just isn't valid. Putting 'field' after a type name in a variable declaration makes as much sense as 'private int class;'
Part of why C# has been so successful in introducing new contextual keywords is that they've been there all along. I think C# 1.0 was ahead of the game on that, and it's interesting how much contextual keywords have started being a bigger tool in language design since C# (all of ES3 of ES4 and some of ES5 were predicated on keywords are always keywords and ES6/ES2015 is where you first start to the shift in JS to a broader contextual keyword approach which seems equal parts inspired by C# as not).
That said, they will also throw compiler warnings in console during build if you are using an all lowercase word with some small number of characters. I don't remember the exact trigger or warning, but it says something like "such words may be reserved for future use by the compiler" to disincentivize use.