function fn1(){console.log(1);}

function fn2(){console.log(2);}

fn1.call.call.call.call(fn2); //=>fn2() =>2

解释：

fn2.call( fn1 ) => fn1.fn2() 

fn1.call=>function call() { [native code] }

fn2.call === fn1.call = Function.call,

Function.call.call( fn2 ) => fn2.call() => fn2() //2

fn1.call.call.call.call(fn2)== Function.call.call.call.call(fn2)//2

=》Function.call.call.+n+.call.call(fn2)//2

=》Function.call.call( fn2 )//2 js运行模式

=》fn2.call()//2

=》fn2()// this === null 或 windows

 

Function.call(fn2)//chrome =>function anonymous() {}

Function(fn2)  //function anonymous() {function fn2(){console.log(2);}}