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Differences between "null" and "undefined" keywords?

Nuno Pereira on August 29, 2019

They both represent a empty value. Difference nr 1! When you define a variable but not assign a value to it, it automatically puts a pl...

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James Thomson • Aug 29 '19 • Edited

Null and undefined are both primitives and falsy values. However null is also an object.

And this is why no one will ever fully understand JavaScript 😆

Even taken from MDN:

The value null represents the intentional absence of any object value. It is one of JavaScript's primitive values.

And when you click through to primitive values, MDN states:

In JavaScript, a primitive (primitive value, primitive data type) is data that is not an object and has no methods.

Yet, typeof null // object 🤔

What the what 🤯

Vlastimil Pospichal • Aug 29 '19 • Edited

anna = {}
bill = {}

anna.age = null
bill.age = null
console.log(anna.age == bill.age)  // ???
console.log(anna.age === bill.age)  // ???

anna.age = NaN
bill.age = NaN
console.log(anna.age == bill.age)  // ???
console.log(anna.age === bill.age)  // ???

emptyother • Aug 30 '19

The new optional parameter for ES6 only cares about undefined.

function myFunc(a, b = 0) { console.log(a,b); }
myFunc(1); // 1 0
myFunc(1,null); // 1 null
myFunc(1,undefined); // 1 0
myFunc(1,getSomeNonExistingValue()); // 1 (null or 0)

Wouldn't it be simpler to use undefined instead of null everywhere? Just stop using null?