There is a new TSLint rule to detect for-in use for arrays that I think would make sense to enable. We have only few violations.

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in#Array_iteration_and_for...in and keep in mind that for-in may inherit properties from Object.

@alexr00 @dbaeumer