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console.log( null === undefined )

Rule

An important rule of checking type with null or undefined is that in the equality equation above, the result will be true only if both sides are either null or undefined.

This is helpful in checking against falsy values such as following -

let c;
console.log(c == null);
// true

console.log(c == undefined);
// true

console.log(0 == null);
// false

console.log("" == null);
// false

One caveat: == should be rarely used. This is a good use case for when == can be used. If you are unsure whether to use == or ===, use ===.

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