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Javascript Variable History

I recently answered a Stackoverflow Question where a user wanted to know if there was a way, in JavaScript, to check if a variable has ever been a particular value.  Of course, there is no default built-in way to do this, but I provided (what I think to be) a valid answer.  However, after a few minutes, I looked at it and thought that it might be able to help other people as well.  So here it is - Chronicle.  Chronicle lets you define a special type of object, and you can check the history of that object at any point in time.  Here's a quick example:

var isValid = new Chronicle(false); // Default the value to false

isValid.set("not valid"); // Set it to a string
isValid.set(true); // Set it to true

// This will return true if the value inside this Chronicle
// has ever been true, and return false otherwise.
isValid.was(false);

If anyone wants this functionality on your site, it's as easy as including/running the following javascript anywhere before you need to use a Chronicle (as long as it's within the proper scope, of course). Chronicle works in any scope, in any situation.

function Chronicle(val){
    this.value = val;
    this.history = [];
    if(val != undefined){
        this.history.push(val);
    }
}

Chronicle.prototype.set = function(val){
    this.value = val;
    this.history.push(val);
};

Chronicle.prototype.was = function(val){
    return this.history.indexOf(val) >= 0;
};

Chronicle.prototype.toString = function(){
    return this.value.toString();
}