The never type essentially represents a value that never occurs, effectively causing an error if it is ever defined.
| let x: never = true; // Error: Type ‘boolean’ is not assignable to type ‘never’. |
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The never type is seldom used on its own and is primarily employed in advanced generics. |
undefined and null are types that correspond to the JavaScript primitives undefined and null, respectively.
| let y: undefined = undefined; let z: null = null; |
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These types are most useful when strictNullChecks is enabled in the tsconfig.json file. |