Math.max.apply first parameter

JavaScript
#1

Tell us what’s happening:

Why null is set as first parameter, when I put any number there like Math.max.apply(100, arr); it also works. What is the purpose of this first argument?

Your code so far

var arr = [6, 89, 3, 45];
var maximus = Math.max.apply(null, arr); // returns 89

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User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:80.0) Gecko/20100101 Firefox/80.0.

Challenge: Use the Spread Operator to Evaluate Arrays In-Place

Link to the challenge:

#2

It isn’t super important to get into the weeds of using .apply() this way, because ES6 introduced a better way to do it (which is the real topic of this challenge).
That said…

Syntax

.apply(thisArg, [ argsArray])

Parameters

thisArg

The value of this provided for the call to func .

Note that this may not be the actual value seen by the method: if the method is a function in non-strict mode code, null and undefined will be replaced with the global object, and primitive values will be boxed. This argument is required.

argsArray Optional

An array-like object, specifying the arguments with which func should be called, or null or undefined if no arguments should be provided to the function.

#3