How do I change multiple elements with same class name using Javascript?

Question

Follow up to my previous question - I want to use a button to show / hide multiple elements with the same class name using JS, yet it appears that I can only change the first element with a certain class name, and all further elements with the same class on the page are ignored.

How do I fix this?

	function designInfo() {
		document.getElementsByClassName("design")[0].style.display = "block";
		document.getElementsByClassName("it")[0].style.display = "none";
		document.getElementsByClassName("other")[0].style.display = "none";
	}

	function itInfo() {
		document.getElementsByClassName("design")[0].style.display = "none";
		document.getElementsByClassName("it")[0].style.display = "block";
		document.getElementsByClassName("other")[0].style.display = "none";
	}
	
	function allInfo() {
		document.getElementsByClassName("design")[0].style.display = "block";
		document.getElementsByClassName("it")[0].style.display = "block";
		document.getElementsByClassName("other")[0].style.display = "block";
	}

    .it {}
    .design {}
    .other {}

    .indent {
      margin: .5em 1em .5em 1em;
    }

    <button onclick="designInfo()">show design stuff</button>
    <button onclick="itInfo()">show IT stuff</button>
    <button onclick="allInfo()">show all</button>

    <div class="indent">

       <div class="it">• boring IT stuff</div>
       <div class="design">• cool design stuff</div>
       <div class="it">• it stuff and things</div>
       <div class="design">• design stuff</div>
       <div class="it">• it stuff and more</div>
       <div class="other">• more it stuff</div>
       <div class="other">• it stuff</div>
  
    </div>

Answer 1

You need to use a for-loop over all items you get from document.getElementsByClassName() method as in following snippet:

function setDisplay(className, displayValue) {
  var items = document.getElementsByClassName(className);
  for (var i=0; i < items.length; i++) {
    items[i].style.display = displayValue;
  }
}

function designInfo() {
  setDisplay("design", "block");
  setDisplay("it", "none");
  setDisplay("other", "none");
}

function itInfo() {
  setDisplay("design", "none");
  setDisplay("it", "block");
  setDisplay("other", "none");
}

function allInfo() {
  setDisplay("design", "block");
  setDisplay("it", "block");
  setDisplay("other", "block");
}

.it {}
.design {}
.other {}

.indent {
  margin: .5em 1em .5em 1em;
}

<button onclick="designInfo()">show design stuff</button>
<button onclick="itInfo()">show IT stuff</button>
<button onclick="allInfo()">show all</button>

<div class="indent">

   <div class="it">• boring IT stuff</div>
   <div class="design">• cool design stuff</div>
   <div class="it">• it stuff and things</div>
   <div class="design">• design stuff</div>
   <div class="it">• it stuff and more</div>
   <div class="other">• more it stuff</div>
   <div class="other">• it stuff</div>

</div>

---

Update Also, it could be written with less code as below:

function filter(designDisp, itDisp, otherDisp) {
  setDisplay("design", designDisp);
  setDisplay("it", itDisp);
  setDisplay("other", otherDisp);
}

function setDisplay(className, displayValue) {
  var items = document.getElementsByClassName(className);
  for (var i=0; i < items.length; i++) {
    items[i].style.display = (displayValue? "block" : "none");
  }
}

.it {}
.design {}
.other {}

.indent {
  margin: .5em 1em .5em 1em;
}

<button onclick="filter(1,0,0)">show design stuff</button>
<button onclick="filter(0,1,0)">show IT stuff</button>
<button onclick="filter(1,1,1)">show all</button>

<div class="indent">

   <div class="it">• boring IT stuff</div>
   <div class="design">• cool design stuff</div>
   <div class="it">• it stuff and things</div>
   <div class="design">• design stuff</div>
   <div class="it">• it stuff and more</div>
   <div class="other">• more it stuff</div>
   <div class="other">• it stuff</div>

</div>