Get all LI elements in array

QuerySelectorAll will get all the matching elements with defined selector. Here on the example I've used element's name(li tag) to get all of the li present inside the div with navbar element.

    let navbar = document
      .getElementById("navbar")
      .querySelectorAll('li');

    navbar.forEach((item, index) => {
      console.log({ index, item })
    });

   
<div id="navbar">
 <ul>
  <li id="navbar-One">One</li>
  <li id="navbar-Two">Two</li>
  <li id="navbar-Three">Three</li>
  <li id="navbar-Four">Four</li>
  <li id="navbar-Five">Five</li>
 </ul>
</div>

If you want all the li tags in an array even when they are in different ul tags then you can simply do

var lis = document.getElementByTagName('li'); 

and if you want to get particular div tag li's then:

var lis = document.getElementById('divID').getElementByTagName('li'); 

else if you want to search a ul first and then its li tags then you can do:

var uls = document.getElementsByTagName('ul');
for(var i=0;i<uls.length;i++){
    var lis=uls[i].getElementsByTagName('li');
    for(var j=0;j<lis.length;j++){
        console.log(lis[j].innerHTML);
    }
}

var allElmnts = document.querySelectorAll("ul");
var arr = []; 
arr.length = allElmnts.length; 
for(var i = 0; i < allElmnts.length; i++){

    arr[i] = allElmnts[i]; 

}