Code Inspection: Unsound type guard check

Reports a typeof or instanceof unsound type guard check. The typeof x type guard can be unsound in one of the following two cases:

typeof x never corresponds to the specified value (for example, typeof x === 'number' when x is of the type 'string | boolean')
typeof x always corresponds to the specified value (for example, typeof x === 'string' when x is of the type 'string')

The x instanceof A type guard can be unsound in one of the following two cases:

The type of x is not related to A
The type of x is A or a subtype of A

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Last modified: 16 July 2021