Null/Undefined Check

In react, if we declare and do not initialise a variable, it would be undefined

var a; //undefined

If we would want to assign a variable and initialise a variable later, we could first assign it as null. (Not recommended)

var a = null;

As undefined and null is different, we should perform validation whenever we think that the code would break if the variable is null or undefined.

typeof null          // "object" (not "null" for legacy reasons)
typeof undefined     // "undefined"

To make the code reusable, we could define a utility function to perform the validation. The function could be as simple as a function that takes in any type of input, or a function that utilise Generics.

function nonNullish(value: unknown): boolean {
    return value !== (null || undefined) ? true : false;  
}


function assertNonNullish<TValue>(value: TValue): boolean {
    return value !== (null || undefined) ? true : false;  
}