How to use JavaScript to complete the copy function?

With preventDefault(), you can use the href of your link because default action should not be taken as it normally would be.

Then you will need to use clipboard API and clipboard.writeText() to make it work.

function clipboardCopy(event) {
    event.preventDefault();
    navigator.clipboard.writeText(event.target.getAttribute('href')).then(() => {
      console.log('clipboard saved url :' + event.target.getAttribute('href'));
    }, () => {
      console.log('clipboard saved url : failed...');
    });
}
a{
  display: block;
  width: 60px;
  height: 60px;
  background-color: #ccc;
  line-height: 60px;
  text-align:center;
}
<a href="https://chickpt.com.tw/dl?tp=4&um=1&ti={{$formatted_job['id']}}&e=share_job"  class="job_info_share_paperlink" onclick="clipboardCopy(event)">copy</a>

function copyJoblink(jobLink) {
    navigator.clipboard.writeText(jobLink);

  /* Alert the copied text */
  alert("Copied the text: " + jobLink);
}
a{
  display: block;
  width: 60px;
  height: 60px;
  background-color: #ccc;
  line-height: 60px;
  text-align:center;
}
<a href="javascript:;"  class="job_info_share_paperlink" onclick="copyJoblink('https://chickpt.com.tw/dl?tp=4&um=1&ti={{$formatted_job[\'id\']}}&e=share_job')">copy</a>

You can do it Like below Tested on Chrome and Microsoft Edge and it is working fine:

function copyJoblink(joblink) {                
  const input = document.createElement('input');
  input.value = joblink;
  document.body.appendChild(input);
  input.focus();
  input.select();
  document.execCommand("copy");
  
  document.body.removeChild(input);

  alert('Link Copied: ' + joblink);
}
a {
  display: block;
  width: 60px;
  height: 60px;
  background-color: #ccc;
  line-height: 60px;
  text-align:center;
}
<a href="javascript:void(0);" class="job_info_share_paperlink" onclick="copyJoblink('https://chickpt.com.tw/dl?tp=4&um=1&ti={{$formatted_job[\'id\']}}&e=share_job')">copy</a>