覆盖Javascript中的全局函数

Question

After overriding the Array function, why the behavior of the two objects is different?

 function Array(){} var array1 = ['1','2'] var array2 = new Array(); console.log(array1.length); // 2 console.log(array2.length); // undefined 

Also, Object() returns an empty object instance but with a user-defined function, we must use new operator, why?

Answer 1

That ( Object() without new ) is a shortcut, which you can provide too:

 function Stuff(x){ if(!(this instanceof Stuff)){ console.log("You forgot 'new'"); return new Stuff(x); } this.x=x; } var a=Stuff(1); var b=new Stuff(2); console.log(a,b); 

And yes, when you locally override the built-in Array , you are stuck with that one. But already existing arrays remain to be original, they do not get fitted retroactively to your own type, and the [] syntax is not affected by your override (case of c ):

 var a=[1,2]; var b=new Array(3,4); (function(){ function Array(){} var c=[1,2]; var d=new Array(3,4); console.log("a:",a); console.log("b:",b); console.log("c:",c); console.log("d:",d); })() 

(The function-magic is necessary for b to remain unaffected by function hoisting)