I want all panels open when the page is loaded and it works. However, the sign must be - when the page is loaded but sign is displayed. After click the , it changed to -, then closed the panel with another click. I want to display the - sign when the page is loaded. Please help me. Thanks!

var acc = document.getElementsByClassName("accordion");
var i;

for (i = 0; i < acc.length; i  ) {
  acc[i].addEventListener("click", function() {
    this.classList.toggle("active");
    var panel = this.nextElementSibling;
    if (panel.style.display === "block") {
      panel.style.display = "none";
    } else {
      panel.style.display = "block";
    }
  });
}

.accordion {
  background-color: #eee;
  color: #444;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
  transition: 0.4s;
}

.active, .accordion:hover {
  background-color: #ccc; 
}

.panel {
  padding: 0 18px;
  display: block;
  background-color: white;
  overflow: hidden;
}

.accordion:after {
  content: '\02795'; /* Unicode character for "plus" sign ( ) */
  font-size: 13px;
  color: #777;
  float: right;
  margin-left: 5px;
}

.active:after {
  content: "\2796"; /* Unicode character for "minus" sign (-) */
}

<button >Section 1</button>
<div >
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

<button >Section 2</button>
<div >
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

<button >Section 3</button>
<div >
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

CodePudding user response：

Few changes here -

1. Add an active class to all the accordion buttons, like this -

   <button >Section 1</button>

2. If the class exists in the classList then classList.toggle(class) removes the class and returns false, else add the class and returns true. so, we can use this return value to show/hide the panel.

var acc = document.getElementsByClassName("accordion");
var i;

for (i = 0; i < acc.length; i  ) {
  acc[i].addEventListener("click", function() {
    const active = this.classList.toggle("active");
    var panel = this.nextElementSibling;
    if (!active) {
      panel.style.display = "none";
    } else {
      panel.style.display = "block";
    }
  });
}

.accordion {
  background-color: #eee;
  color: #444;
  cursor: pointer;
  padding: 18px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
  transition: 0.4s;
}

.active, .accordion:hover {
  background-color: #ccc; 
}

.panel {
  padding: 0 18px;
  display: block;
  background-color: white;
  overflow: hidden;
}

.accordion:after {
  content: '\02795'; /* Unicode character for "plus" sign ( ) */
  font-size: 13px;
  color: #777;
  float: right;
  margin-left: 5px;
}

.active:after {
  content: "\2796"; /* Unicode character for "minus" sign (-) */
}

<button >Section 1</button>
<div >
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

<button >Section 2</button>
<div >
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>

<button >Section 3</button>
<div >
  <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
</div>