JS変換タイムスタンプは「ただいま」、「1分前」、「2時間前」、「1日前」などです.

var minute = 1000 * 60;
var hour = minute *60;
var day = hour *24;
var week = day * 7;
var month = day * 30;
function getTimer(stringTime){
    var time1 = new Date().getTime();//      
    console.log(time1);
    var time2 = Date.parse(new Date(stringTime));//        
    console.log(time2);
    var time = time1 - time2;

    var result = null;
    if(time < 0){
        alert("             ！");
    }else if(time/month >= 1){
        result = "   " + parseInt(time/month) + "  ！";
    }else if(time/week >= 1){
        result = "   " + parseInt(time/week) + "  ！";
    }else if(time/day >= 1){
        result = "   " + parseInt(time/day) + "  ！";
    }else if(time/hour >= 1){
        result = "   " + parseInt(time/hour) + "   ！";
    }else if(time/minute >= 1){
        result = "   " + parseInt(time/minute) + "   ！";
    }else {
        result = "    ！";
    }
    console.log(result);
}
getTimer("2015-07-20 15:21:12");