The history of “typeof null”
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In JavaScript, typeof null is 'object', which incorrectly suggests that null is an object (it isn’t, it’s a primitive value, consult my blog post on categorizing values for details). This is a bug and one that unfortunately can’t be fixed, because it would break existing code. Let’s explore the history of this bug.
The “typeof null” bug is a remnant from the first version of JavaScript. In this version, values were stored in 32 bit units, which consisted of a small type tag (1–3 bits) and the actual data of the value. The type tags were stored in the lower bits of the units. There were five of them:
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