方法作为javascript中对象的属性

Question

i need to create a javascript function with a private variable that has setter and getter methods. i tried:

function createSecretHolder(secret) {
  this._secret = secret;
  var getSecret = function(){
    return this._secret;
  }
  var setSecret = function(secret){
    this._secret = secret;
  }
}

and a version with:

this.getSecret = function()...

and

this.seSecret = function()...

it is not passing the test suite on code wars. something like

var obj = createSecretHolder(secret);
obj.getSecret();
obj.setSecret(newSecret);

and others which are hidden. I get an error TypeError: Cannot read property 'getSecret' of undefined and another cannot call method setSecret

Answer 1

createSecretHolder() doesn't return a value so createSecretHolder(secret) returns undefined .

So var obj = createSecretHolder(secret); sets obj to undefined. Hence the error "Cannot read property 'getSecret' of undefined" when you try to access obj.getSecret() .

Even if it returned an object, you have declared getSecret using var inside a function . Variables described that way are scoped to the function. So when you try to access it outside the function, as you do in obj.getSecret() , that won't work.

You also seem to misunderstand how this works. It will not create a private variable.

There are a number of ways to do this. Here's one:

function createSecretHolder(mySecret) {
    var secret = mySecret;
    return {
      getSecret: function(){
        return secret;
      },
      setSecret: function (mySecret){
        secret = mySecret;
      }
    };
}

Answer 2

When you use a Constructor to create an object you need to use the new keyword.

Inside your constructor you set a property with this._secret = secret . This is accessible from outside. It should be var _secret = secret .

Also you create local functions inside your object to get/set _secret . They should be methods of the object. See below.

// object constructor
function createSecretHolder(secret) {
    // local variable. it isn't accessible from outside
    var _secret = secret;
    // method to get the secret
    this.getSecret = function() {
        return _secret;
    }
    // method to set the secret
    this.setSecret = function(secret){
        _secret = secret;
    }
}
// create new "createSecretHolder" object
var secret = new createSecretHolder("secret 1");

secret.getSecret(); // returns "secret 1"
secret.setSecret("secret 2");
secret.getSecret(); // returns "secret 2"

Answer 3

Look into prototypejs OO programming.

If you can't use prototypejs because of jQuery conflicts, there is a version of it only with OO support here: https://github.com/Prescia/Prototypejslt

Your could would look like:

createSecretHolder= Class.create();
createSecretHolder.prototype = {
    _secret: 0,
    othervariable: true,
    initialize: function(inSecret) { // this is the constructor on prototypejs
        this._secret = inSecret;
    }
}

// Create instance:
var myInstance = new createSecretHolder(5);
// so this should alert "5":
alert(myInstance._secret);

I can't live without prototypejs Object Orientation, so I often use this light version that won't conflict with other stuff