Sử dụng Union Any Void Never any void never trong TypeScript

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let code: (string | number);
code = 123;   // OK
code = "ABC"; // OK
code = false; // Compiler Error

let empId: string | number;
empId = 111; // OK
empId = "E111"; // OK
empId = true; // Compiler Error

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function displayType(code: (string | number))
{
    if(typeof(code) === "number")
        console.log('Code is number.')
    else if(typeof(code) === "string")
        console.log('Code is string.')
}

displayType(123); // Output: Code is number.
displayType("ABC"); // Output: Code is string.
displayType(true); //Compiler Error: Argument of type 'true' is not assignable to a parameter of type string | number

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let something: any = "Hello World!"; 
something = 23;
something = true;

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var something = "Hello World!";
something = 23;
something = true;

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let arr: any[] = ["John", 212, true]; 
arr.push("Smith"); 
console.log(arr); //Output: [ 'John', 212, true, 'Smith' ] 

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function sayHi(): void { 
    console.log('Hi!')
} 

let speech: void = sayHi(); 
console.log(speech); //Output: undefined

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function throwError(errorMsg: string): never { 
            throw new Error(errorMsg); 
} 

function keepProcessing(): never { 
            while (true) { 
         console.log('I always does something and never ends.')
     }
}