JS Battery Level Monitor SRC

<script>
navigator.getBattery().then(function(battery) {
document.writeln('Current Charge Level: '+battery.level);
battery.onlevelchange = function() {
if(this.level==1.0){
alert('Battery Is Fully Charged!!')
}
if(this.level==0.1){
alert('Battery Is Almost Dead!!');
}
}
});
</script>