How do I check a variable I receive latter different than the previous one

Is there anyway to check that a variable value I receive latter different than the previous one as below:

function passData() {
   var i = Math.random();
   getData(i);
}

function getData(i) {
   this.i = i;
   console.log(i);
}

var button = document.getElementById('button');
button.addEventListener('click', passData, false);

Code (markup):

In real life there is only two values of variable being received through websocket and I don't know how to separate them.
Thank you,

 

I did it. Put them in an array.

 

yes you can use array, but if you need to compare only with the last value, then you can use a variable.
for example

var lastvalue=0;
function actionXYZ(value){
  // perform comparison of 'value' to 'lastvalue'

//do action

// in the end, update lastvalue
lastvalue=value;
}

HTML: