以下Javascript语句有什么问题？

Question

The following code gives error.

var user;

user.load= function () {

//

}

It gives error Cannot read property 'load' of undefined

EDIT: Isn't everything an Object by default in Javascript?

Answer 1

The user variable needs to be an object in order for you to assign properties to it. Variables that have not been assigned a value are undefined , and you can't assign properties to undefined .

var user = {};
user.load = function () {
    // ...
}

Answer 2

try this:

var user = {};

user.load= function () {

//

}

Answer 3

var user = {};
user.load= function () {

//

} 

At the moment user is undefined , where it needs to be an object.

Answer 4

var user = {
   load: function(){
        return 'hi';
   }
};
user.load();

or

var user = function(){
   this.load = function(){
      return 'Hi';
   }
}

Answer 5

Isn't everything an Object by default in Javascript?

No. Many things are objects, but the default value of a variable is undefined , and that is is a primitive which cannot be assigned properties.

You need to assign an object (a new empty object is fine) to the variable:

var user = {};