CODEWITHSUNDEEP
javascriptoopprototype
prettymuchbryce
prettymuchbryce

Reputation: 131

Javascript public method parameters as private vars

I am trying to figure out how to have a private instance variable on my class that gets set by a parameter of a public method. In this case, though; it seems that outside of somePublicMethod myPrivateVar will be undefined. How can achieve what I am trying to do ?

MyClass = function() {
    var myPrivateVar;

    this.somePublicMethod(myPrivateVar) {
        myPrivateVar = myPrivateVar //????
    }

    this.someOtherPublicMethod() {
        somePrivateMethod();
    }

    function somePrivateMethod() {
        myPrivateVar++;
    }
}

Upvotes: 1

Views: 321

Answers (3)

Sampson
Sampson

Reputation: 268364

Have you considered taking a slightly different route?

var MyClass = function(){
    var bar = "private";
    return {
        setBar: function( newBar ) { bar = newBar; },
        getBar: function() { return bar; }
    }
};

When you new-up an instance of this class, the bar property will be private. However, it will still be accessible by the public setBar and getBar methods.

var inst = new MyClass;

console.log( inst.bar ); // undefined
console.log( inst.getBar() ); // 'private'

inst.setBar( 'accessible' );

console.log( inst.getBar() ); // 'accessible'

Upvotes: 0

Jonathan Lonowski
Jonathan Lonowski

Reputation: 123473

The issue is you're shadowing the var myPrivateVar by giving the argument the same name, so only the argument variable is in scope:

this.somePublicMethod = function(myPrivateVar) {
    myPrivateVar = myPrivateVar; // sets the argument to itself
}

You'll need to give one of them a different name to avoid shadowing:

this.somePublicMethod = function(inputVar) {
    myPrivateVar = inputVar;
};

Otherwise, you'll need to contain one of them somehow:

MyClass = function () {
    var locals = {
        myPrivateVar: null
    };

    this.somePublicMethod = function (myPrivateVar) {
        locals.myPrivateVar = myPrivateVar;
    };

    function somePrivateMethod() {
        locals.myPrivateVar++;
    }
};

Upvotes: 2

João Silva
João Silva

Reputation: 91329

Use this.myPrivateVar:

this.somePublicMethod = function(myPrivateVar) {
    this.myPrivateVar = myPrivateVar;
}

To call the private method within the context of this, you can use:

this.somePublicMethod = function(myPrivateVar) {
    this.myPrivateVar = myPrivateVar;
    somePrivateMethod.call(this); // pass this as the context of the private method
}

function somePrivateMethod() {
    this.myPrivateVar++;
}

Upvotes: 1

Related Questions