Return on ad spend (ROAS)

<div class="calc"><div class="head">REVENUE <strong>$400</strong></div><label for="spend">AD SPEND <output id="amount">$100</output></label><input id="spend" type="range" min="50" max="300" step="10" value="100"><div class="result"><span>ROAS</span><b id="roas">4.0×</b></div></div>

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const input=document.querySelector('#spend'),amount=document.querySelector('#amount'),roas=document.querySelector('#roas');function update(){amount.textContent='$'+input.value;roas.textContent=(400/Number(input.value)).toFixed(1)+'×'}input.addEventListener('input',update);let v=100,step=10;const timer=setInterval(()=>{if(document.activeElement===input){clearInterval(timer);return}v+=step;if(v>=250||v<=80)step*=-1;input.value=String(v);update()},650);