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Private in JavaScript

November 18, 2008
Tagged closure, JavaScript, private

Erik Arvidsson has posted an article about instance private, class private, packages and friends.

Erik stated the traditional methods of setting private members in JavaScript are having some shortcomings:

• Using closure
  Problem with this method is that it consumes more memory as every instances need to have its own copy of function to access its private member.

  function A() {
  var privateMember = "value";
  this.getMember = function() {
  return privateMember;
  }
  }
  

• Using naming convention
  Try to name the private variables as _privateMember (add underscore in the front). Problem is that it actually doesn’t encapsulate the variable at all as you can reference the variable via instances._privateMember.

So what should we do? Erik suggested the key point is actually think seriously about whether the members should be truly private or not:

If you really need to be able to hide the state then I would use the instance private pattern first used in this post. It is easy to write and easy to understand and does not have a lot of boiler plate code. However, I would only use it where hiding the state really matters. In most cases it doesn’t. For example, Gmail was written without any true private members. We just use a naming convention.

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