let counterValue=0;

 bindCounterVal()
function increment(){
counterValue++;
bindCounterVal()
}

function decrement(){
counterValue--;
bindCounterVal()
}
function bindCounterVal(){
validateValue()
document.getElementById('counterVal').innerText=counterValue
}

function validateValue(){
if(counterValue>0){
document.getElementById("decrement-btn").disabled = false;
}else{
document.getElementById("decrement-btn").disabled = true;
}
}

<button onclick="increment()">+</button>
<button id="decrement-btn" onclick="decrement()">-</button>
<h1 id='counterVal'></h1>