Why should you pass Math as the first argument to Math.max.apply?

Question

I'm going through John Resig's JavaScript ninja tutorial and on #51 I see this:

// Find the largest number in that array of arguments 
var largestAllButFirst = Math.max.apply( Math, allButFirst ); 

allButFirst is just a small array of integers. I believe I understand what apply does, but I can't understand why Math is being passed as an argument to apply.

Answer 1

The first parameter of the .apply is the context. Inside the function body the this keyword will reference that value.

Example:

function sum(a){ return this + a; }
sum.apply(1, [1]); // will return 2
// or with .call
sum.call(1, 1); // also returns 2

By default if you call Math.max the context (the this keyword) is automatically set to Math. To keep this behavior Math is passed as the first parameter in apply.

Answer 2

Passing it Math is not necessary, anything will work here. Math indicates the context of the operation, however max does not require a context. This means that Math.max.apply(undefined, allButFirst) will also work. See this answer.