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Code Inspection: Unsound type guard check

typeof x type guard can be unsound in one of the following two cases:

  1. typeof x never corresponds to the specified value (e.g., typeof x === 'number' when x has type 'string | boolean')

  2. typeof x always corresponds to the specified value (e.g., typeof x === 'string' when x has type 'string')


x instanceof A type guard can be unsound in one of the following two cases:
  1. Type of x is not related to A

  2. Type of x is A or a subtype of A

Last modified: 10 February 2020