How to reset this JS object?

Question

Here I want to reset all properties of Data to their original values, how I do that?

var Data = {
  prop1: false,
  prop2: true,
  prop3: null
}

Some code executes & sets Data.prop1 = "abc";

I never instantiated Data, is that a problem?

Answer 1

Data is a dynamic object. You could just add a function that will reset all the values:

var Data = {
    prop1: false,
    prop2: true,
    prop3: null,
    reset: function () {
        this.prop1 = false;
        this.prop2 = true;
        this.prop3 = null;
    }
}

Answer 2

Another way to do it would be this:

var Data = {
  prop1: false,
  prop2: true,
  prop3: null,

  // save initial values
  init: function() {
      var origValues = {};
      for (var prop in this) {
          if (this.hasOwnProperty(prop) && prop != "origValues") {
              origValues[prop] = this[prop];
          }
      }
      this.origValues = origValues;
  },
  // restore initial values
  reset: function() {
      for (var prop in this.origValues) {
          this[prop] = this.origValues[prop];
      }
  }
}

Then, when you use it, you call Data.init() in your initialization code to save the current values so they can be restored later with Data.reset(). This has the advantage that maintenance is easier. When you add or change a variable to your data structure, it is automatically incorporated into the reset function without you having to make any specific changes.

You can see it work here: http://jsfiddle.net/jfriend00/EtWfn/.

Answer 3

The simplest way that avoids having to duplicate all of the default values is to just use a more traditional constructor and instantiate your Data object from there. Then when you need to reset you can just throw away your old object and instantiate a new one.

Note: in the following code I've used the JS convention that functions intended to be used as object constructors start with an uppercase letter, and the variable referencing an instance starts with lowercase.

function Data() {
   this.prop1 = false;
   this.prop2 = true;
   this.prop3 = null;
}

var data = new Data();

data.prop1 = "abc"; // change some properties of data
data.prop3 = "something else";

data = new Data();  // "reset" by getting a new instance

If you don't like having to use "new" you could just write a non-constructor style function that returns an object:

function getData() {
   return {
      prop1: false,
      prop2: true,
      prop3: null
   };
}

var data = getData();
data.prop1 = "abc";

data = getData();  // reset

If for some reason you need the reset to keep the same actual instance rather than getting a new identical one then you will need to change the properties back one by one as per Frits van Campen's answer (you'd also need to add some code to delete any extra properties that were added along the way).