var toplama_islemi = (document.getElementById("toplama_islemi").style.display ="none");
var cıkarma_islemi = (document.getElementById("cıkarma_islemi").style.display ="none");
var carpma_islemi = (document.getElementById("carpma_islemi").style.display ="none");
var bolme_islemi = (document.getElementById("bolme_islemi").style.display ="none");
And why are there two equal signs here?
Those aren't comparisons. They're assignments. The styles are applied to the elements, and then the elements' style property values are assigned to variables.
Here's a demonstration.
setTimeout(function() {
var toplama_islemi = (document.getElementById("toplama_islemi").style.display = "none");
var cıkarma_islemi = (document.getElementById("cıkarma_islemi").style.display = "none");
var carpma_islemi = (document.getElementById("carpma_islemi").style.display = "none");
var bolme_islemi = (document.getElementById("bolme_islemi").style.display = "none");
console.log({toplama_islemi, cıkarma_islemi, carpma_islemi, bolme_islemi});
}, 2000);<p>Wait for it...</p>
<div id="toplama_islemi">toplama_islemi</div>
<div id="cıkarma_islemi">cıkarma_islemi</div>
<div id="carpma_islemi">carpma_islemi</div>
<div id="bolme_islemi">bolme_islemi</div>Everything is an object in JavaScript (except primitive values). If you don't want the style property values returned, do the steps separately:
var toplama_islemi = document.getElementById("toplama_islemi");
toplama.style.display = "none";
Now the element is assigned to the variable instead.