JavaScript：默认对象的属性和方法

Question

As you know, in javascript functions are objects, my problem is with the following code:

function Car() {
 this.color = "black";
}
console.log(Car.name);
console.log(Car.color);

Output : Car undefined

Since I could access name property of Car object why can't I access color property of Car object in the same way.

Another example:

console.log("Hello".charAt.name);
console.log("Hello".charAt.length);  

Output : charAt 1

Here charAt is a method of String object but I used its name as a reference to access name and length properties and not only these properties but also some methods such as : hasOwnProperty and isPrototypeOf

My question is what exactly those properties and methods?

Answer 1

In class terms, name is a property of the class Car whereas color is a property of an instance of the class Car . You can only access the color property when you create a new instance of it.

 function Car() { this.color = "black"; } var car = new Car() document.write(Car.name +'<br>'); document.write(car.color +'<br>'); 

Answer 2

in your first example you're trying to access the property color of function Car ;

 function Car() { this.color = "black"; console.log(this)//Window {} }; /*you need to set Car.color */ Car.color = 'white'; console.log(Car.name);//Car console.log(Car.color);//white Car(); console.log(color)//black //Car //white //Window {} //black 

while name property is set automatically in function declarations..

when called normally, in a non strict situation, this inside the function refers to Window object ( which is global on browser );

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on the other hand if you call the function as a constructor this refers to return object:

 function Car() { this.color = "black"; console.log(this) //object instance assigned to mazda }; var mazda = new Car(); console.log(mazda.color)