CODEWITHSUNDEEP
javascript
Jake Sellers
Jake Sellers

Reputation: 2439

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

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.

Upvotes: 6

Views: 304

Answers (3)

László
László

Reputation: 872

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.

Upvotes: 3

Davin Tryon
Davin Tryon

Reputation: 67316

From Mozilla docs:

fun.apply(thisArg, [argsArray])

thisArg: The value of this provided for the call to fun. 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.

So, in your example, Math is being used as the context for the function (if the keyword this is used inside).

If no thisArg is used, then the default is the global object. So, it is good practice to give some context if possible.

Upvotes: 0

PlasmaPower
PlasmaPower

Reputation: 1878

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.

Upvotes: 1

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