浏览器内置的function很多
Manth.random()
In fact, some of the code you are calling when you invoke(a fancy word for run, or execute) a built in browser function couldn't be written in JavaScript -- many of these functions are calling parts of the background browser code, which is written largely low-level system languages like C++, not web languages like JavaScript.

invoke  (a fancy word for run, or execute)援引;援用(法律、规则等作为行动理由);提及(某人、某理论、实例等作为支持);提出(某人的名字，以激发某种感觉或行动)。

很多内置的浏览器function并不属于JavaScript语言的core， 其中一些是browser的APIS，还有些第三方APIs

Functions versus methods

函数function是对象的方法methods.