Regular Expression Pattern: <([a-zA-Z]+)(?
![^>]*\/>)>

const regex = /<([a-zA-Z]+)(?
![^>]*\/>)>/; 

const inputString =  
    '<div><br/><p>Hello</p><span>World</span></div>'; 
const matches = inputString.match(regex); 
  
console.log(matches);

[
  '<div>',
  'div',
  index: 0,
  input: '<div><br/><p>Hello</p><span>World</span></div>',
  groups: undefined
]

Regular Expression Pattern: <(div|p|span|...)>

const regex = /<(div|p|span)>/; 
const inputString =  
    '<div><br/><p>Hello</p><span>World</span></div>'; 
const matches = inputString.match(regex); 
  
console.log(matches);

[
  '<div>',
  'div',
  index: 0,
  input: '<div><br/><p>Hello</p><span>World</span></div>',
  groups: undefined
]

parseFromString(string, mimeType);

// Example HTML input 
const Data = 
    '<div class="container"><p>Hello, <span>world!</span></p></div>'; 
  
// Create a DOM parser 
const parser = new DOMParser(); 
  
// Parse the HTML string 
const inputElement = parser.parseFromString(Data, 'text/html'); 
  
// Get all elements 
const elements = inputElement.getElementsByTagName('*'); 
  
// Filter open tags 
const matches = Array.from(elements).filter((element) => 
    element.outerHTML.match(/<([A-Za-z][A-Za-z0-9]*)\b(?
![^>]*\/>)/)); 

  
// Output the matched open tags 
console.log(matches);

(6)   
0: html  
1: head  
2: body  
3: div.container  
4: p  
5: span