JavaScript中对象与对象之间的区别

Question

In the below code :-

 var x = { } ;
    console.log(typeof x);             // o/p is object
    console.log(x instanceof Object ); //o/p is true

If I use " object " instead of " Object " in the last line I get an error.Why is that so when the o/p of second line is object with a lowercase "o"?

Answer 1

Because there's no such thing as an 'object'. Typeof doesn't give you the class back - it gives you back the primitive type that it is. For example, typeof "string" gives you back "string".

The 'Object' is a constructor for an object 'primitive' - so a new Object gives you back an 'object' to work with.. but don't expect to be able to create a 'new object', as an 'object' doesn't exist as a constructor.

Answer 2

You get an error because you haven't defined a variable named object . Attempting to read a variable that has not been declared is a ReferenceError .

The Object variable is native to the environment, and is pre-defined as the constructor function for plain objects. That's why it works when you do instanceof Object . Every native object in JavaScript is an instance of Object .

Answer 3

Javascript is case sensitive "object" is essentially a variable that can hold anything. "Object" is an actual javascript type.