您可以使用foreach

null

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

var expandAll = document.getElementById("expandAll");
var collapseAll = document.getElementById("collapseAll");

expandAll.addEventListener("click", () => {
  Array.from(acc).forEach(p => {
    p.classList.add("active");
    p.nextElementSibling.style.display = "block";
  });
});

collapseAll.addEventListener("click", () => {
  Array.from(acc).forEach(p => {
    p.classList.remove("active");
    p.nextElementSibling.style.display = "none";
  });
});

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: 8px;
  width: 100%;
  text-align: left;
  border: none;
  outline: none;
  transition: 0.4s;
}

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


/* Style the accordion panel. Note: hidden by default */

.panel {
  padding: 0 18px;
  background-color: white;
  display: none;
  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 (-) */
}

.panel ul,
li {
  line-height: 0.5
}

;

<button id="expandAll">Expand All</button>
<button id="collapseAll">Collapse All</button>

<button class="accordion">'test1'</button>
<div class="panel">
  <p>
    <b>"Description :";<br/><br/> </b> "test 1.";<br/><br/>
    <b>"DB :";<br/><br/> </b> "test,\u00A0 \u00A0 \u00A0 tes, \u00A0 \u00A0 \u00A0 test ";<br/><br/>
    <b>"Query:";<br/><br/> </b> "test;";<br/><br/>
    <b>"Additional Information:";<br/><br/> </b> "test.";<br/><br/>
  </p>
</div>

<button class="accordion">'test1'</button>
<div class="panel">
  <p>
    <b>"Description :";<br/><br/> </b> "test 1.";<br/><br/>
    <b>"DB :";<br/><br/> </b> "test,\u00A0 \u00A0 \u00A0 tes, \u00A0 \u00A0 \u00A0 test ";<br/><br/>
    <b>"Query:";<br/><br/> </b> "test;";<br/><br/>
    <b>"Additional Information:";<br/><br/> </b> "test.";<br/><br/>
  </p>
</div>

全部展开的代码

document.querySelectorAll('.panel').forEach(node => node.style.display='block')
document.querySelectorAll('.accordion').forEach(node => node.classList.add('active'))

要折叠的全部代码

document.querySelectorAll('.panel').forEach(node => node.style.display='none')
document.querySelectorAll('.accordion').forEach(node => node.classList.remove('active'))