Add dash automatically in Javascript

When typing, use Phone no xxx-xxx-xxx like 123-456-7890

–JS File

var inputKeys = document.querySelectorAll('input[name="your-phone"]');

for(i=0; i<inputKeys.length; i++){
	inputKeys[i].onkeypress = function(){
		var currentValue = this.value;
		console.log('Lengh ' + currentValue);
		this.value = currentValue;
		if(this.value.toString().length == 3 || this.value.toString().length == 7){
			var newVal = this.value.concat('-');
            this.value = newVal;
		}
    }
}