JavaScript - Ejecutar una condicion cuando una variable aumente

mx:<input id="mx" type="text" value="10" readonly /><br />

x: <input id="x" type="text" value="50" readonly /><br />

<input id="cmdMas" type="button" value="Incrementar" />

<input id="cmdMenos" type="button" value="Decrementar" />

<script>

	document.getElementById('cmdMas').addEventListener('click',calcularMas);

	document.getElementById('cmdMenos').addEventListener('click',calcularMenos);

	function calcularMas(e){

		mx = parseInt(document.getElementById('mx').value);

		x  = parseInt(document.getElementById('x').value);

		if(e.target.id=='cmdMas'){

			mx++;

			x+=5;

		} else if(e.target.id=='cmdMenos'){

			mx--;

			x-=5;

		}

		document.getElementById('mx').value = mx;

		document.getElementById('x').value  = x;

	}

	function calcularMenos(e){

		mx = parseInt(document.getElementById('mx').value);

		x  = parseInt(document.getElementById('x').value);

		mxTmp = mx;

		if(e.target.id=='cmdMas'){

			mx++;

		} else if(e.target.id=='cmdMenos'){

			mx--;

		}

		if( mxTmp<mx ){

			x+=5;

		}else{

			x-=5;

		}

		document.getElementById('mx').value = mx;

		document.getElementById('x').value  = x;

	}

</script>