How does the Math.max.apply() work?

apply accepts an array and it applies the array as parameters to the actual function. So,

Math.max.apply(Math, list);

can be understood as,

Math.max("12", "23", "100", "34", "56", "9", "233");

So, apply is a convenient way to pass an array of data as parameters to a function. Remember

console.log(Math.max(list));   # NaN

will not work, because max doesn't accept an array as input.

There is another advantage, of using apply, you can choose your own context. The first parameter, you pass to apply of any function, will be the this inside that function. But, max doesn't depend on the current context. So, anything would work in-place of Math.

console.log(Math.max.apply(undefined, list));   # 233console.log(Math.max.apply(null, list));        # 233console.log(Math.max.apply(Math, list));        # 233

Since apply is actually defined in Function.prototype, any valid JavaScript function object, will have apply function, by default.

On JavaScript ES6 just use the Spread operator:

var list = ["12","23","100","34","56","9","233"];console.log(Math.max(...list));//                   ^^^ Spread operator 

Can anyone tell me how does the below code work?

Math.max.apply(Math,list)

Invokes a Math.max function with Math object to be used as a this reference in the function implementation (body) and list to be passed as an arguments.

So this eventually equals to

Math.max("12","23","100","34","56", "9","233")

It seems it works if i pass null or Math.

Obviously Math.max implementation doesn't use instance variable - there is no reason to do so. The native implementation would just iterate over arguments and find the maximum one.

Does all the user-defined/Native functions have call and apply method which we can use?.

Yes, every single function can be invoked using call or apply

References:

• MDN .apply() documentation (credits to @RGraham)