How to create tooltip over text selection without wrapping?

Assuming something selected

var selection = window.getSelection(),      // get the selection then
    range = selection.getRangeAt(0),        // the range at first selection group
    rect = range.getBoundingClientRect(); // and convert this to useful data

rect is now a Object which holds the positions relative the the current scroll coordinates of the Window. More info on this here. If you want to be even more precise, you can use getClientRects which returns a list of such Objects, which you would then have to put together to form the area of the selection.

Now, to draw a box around it (I'll take the easy route using fixed for demonstration purposes)

var div = document.createElement('div');   // make box
div.style.border = '2px solid black';      // with outline
div.style.position = 'fixed';              // fixed positioning = easy mode
div.style.top = rect.top + 'px';       // set coordinates
div.style.left = rect.left + 'px';
div.style.height = rect.height + 'px'; // and size
div.style.width = rect.width + 'px';
document.body.appendChild(div);            // finally append

You will probably want to take into consideration the scroll position so you can use absolute positioning. If there are no other scrollable elements, this means you just need to factor in the values of window.scrollX and window.scrollY, which are the position of the window's x and y coordinates in pixels at the time they're accessed.

var div = null;

function drawBorderAroundSelection() {
  var selection = window.getSelection(), // get the selection then
    range = selection.getRangeAt(0), // the range at first selection group
    rect = range.getBoundingClientRect(); // and convert this to useful data

  if (rect.width > 0) {
    if (div) {
      div.parentNode.removeChild(div);
    }
    div = document.createElement('div'); // make box
    div.class = 'rect';
    div.style.border = '2px solid black'; // with outline
    div.style.position = 'fixed'; // fixed positioning = easy mode
    div.style.top = rect.top + 'px'; // set coordinates
    div.style.left = rect.left + 'px';
    div.style.height = rect.height + 'px'; // and size
    div.style.width = rect.width + 'px';
    document.body.appendChild(div); // finally append
  }
}

window.onmouseup = drawBorderAroundSelection;
<p>
  Lorem ipsum dolor sit amet, consectetur adipiscing elit. Donec ut dolor porta neque vulputate auctor et a ligula. Quisque bibendum risus magna, eget feugiat erat faucibus sed. Phasellus sed massa elementum, laoreet ipsum non, dignissim orci. Aenean lobortis
  nunc et purus molestie, vel consectetur ligula dapibus. In ut lorem mattis, commodo nisi aliquam, porta ante. Curabitur sit amet libero sed justo finibus porttitor. Donec ac est ultrices, pretium diam sed, blandit nunc. Morbi consequat finibus augue
  vel ultricies. Vestibulum efficitur ante vitae cursus accumsan. Vestibulum rutrum ex ex, a egestas nisi malesuada eu. Pellentesque fermentum, ante id convallis luctus, tellus lectus viverra diam, sit amet convallis ligula lorem sit amet neque.
</p>

$(document).ready(function () {
  function tweetButtonClick() {
    let selectedText = document.getSelection().toString();
    /*window.open(
      "https://twitter.com/intent/tweet?url=https://www.linkedin.com/in/harsha-vardhan-ch-245197bb/&text=" +
        selectedText
    );*/
    console.log("This is your selected text: ",selectedText);
  }

  const textSelectionTooltipContainer = document.createElement("div");
  textSelectionTooltipContainer.setAttribute(
    "id",
    "textSelectionTooltipContainer"
  );
  textSelectionTooltipContainer.innerHTML = `<button id="textShareTwitterBtn">TWEET</button>`;
  const bodyElement = document.getElementsByTagName("BODY")[0];

  $("body").on("click", "#textShareTwitterBtn", tweetButtonClick);

  bodyElement.addEventListener("mouseup", function (e) {
    var textu = document.getSelection().toString();
    if (!textu.length) {
      textSelectionTooltipContainer.remove();
    }
  });

  document
    .getElementById("textToSelect")
    .addEventListener("mouseup", function (e) {
      let textu = document.getSelection().toString();
      let matchu = /\r|\n/.exec(textu);
      if (textu.length && !matchu) {
        let range = document.getSelection().getRangeAt(0);
        rect = range.getBoundingClientRect();
        scrollPosition = $(window).scrollTop();
        containerTop = scrollPosition + rect.top - 50 + "px";
        containerLeft = rect.left + rect.width / 2 - 50 + "px";
        textSelectionTooltipContainer.style.transform =
          "translate3d(" + containerLeft + "," + containerTop + "," + "0px)";
        bodyElement.appendChild(textSelectionTooltipContainer);
      }
    });
});
#textSelectionTooltipContainer {
  will-change: transform;
  position: absolute;
  width: 100px;
  height: 40px;
  background: #f7d39d;
  top: 0px;
  left: 0px;
  display: flex;
  padding: 5px 10px;
  box-sizing: border-box;
  justify-content: center;
}

#textSelectionTooltipContainer button {
  font-size: 14px;
  border: 1px solid black;
  background: none;
  cursor: pointer;
  margin: 0 2px;
}
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="utf-8">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
  <link rel='stylesheet' href='shareText.css' />
  <title>Text Share Feature</title>
  <script>

  </script>
</head>

<body>
  
  <div id="textToSelect">
  
    <h1>HTML Ipsum Presents</h1>
  
    <p><strong>Pellentesque habitant morbi tristique</strong> senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. <em>Aenean ultricies mi vitae est.</em>    Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, <code>commodo vitae</code>, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci,
      sagittis tempus lacus enim ac dui. <a href="#">Donec non enim</a> in turpis pulvinar facilisis. Ut felis.</p>
  
    <h2>Header Level 2</h2>
  
    <ol>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ol>
  
    <blockquote>
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus magna. Cras in mi at felis aliquet congue. Ut a est eget ligula molestie gravida. Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        elit sit amet quam. Vivamus pretium ornare est.</p>
        <p>
        Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        </p>
    </blockquote>
  
    <h3>Header Level 3</h3>
  
    <ul>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ul>
    <h1>HTML Ipsum Presents</h1>
  
    <p><strong>Pellentesque habitant morbi tristique</strong> senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. <em>Aenean ultricies mi vitae est.</em>    Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, <code>commodo vitae</code>, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci,
      sagittis tempus lacus enim ac dui. <a href="#">Donec non enim</a> in turpis pulvinar facilisis. Ut felis.</p>
  
    <h2>Header Level 2</h2>
  
    <ol>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ol>
  
    <blockquote>
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus magna. Cras in mi at felis aliquet congue. Ut a est eget ligula molestie gravida. Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        elit sit amet quam. Vivamus pretium ornare est.</p>
        <p>
        Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        </p>
    </blockquote>
  
    <h3>Header Level 3</h3>
  
    <ul>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ul>
    <h1>HTML Ipsum Presents</h1>
  
    <p><strong>Pellentesque habitant morbi tristique</strong> senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. <em>Aenean ultricies mi vitae est.</em>    Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, <code>commodo vitae</code>, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci,
      sagittis tempus lacus enim ac dui. <a href="#">Donec non enim</a> in turpis pulvinar facilisis. Ut felis.</p>
  
    <h2>Header Level 2</h2>
  
    <ol>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ol>
  
    <blockquote>
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus magna. Cras in mi at felis aliquet congue. Ut a est eget ligula molestie gravida. Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        elit sit amet quam. Vivamus pretium ornare est.</p>
        <p>
        Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        </p>
    </blockquote>
  
    <h3>Header Level 3</h3>
  
    <ul>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ul>
    <h1>HTML Ipsum Presents</h1>
  
    <p><strong>Pellentesque habitant morbi tristique</strong> senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. <em>Aenean ultricies mi vitae est.</em>    Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, <code>commodo vitae</code>, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci,
      sagittis tempus lacus enim ac dui. <a href="#">Donec non enim</a> in turpis pulvinar facilisis. Ut felis.</p>
  
    <h2>Header Level 2</h2>
  
    <ol>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ol>
  
    <blockquote>
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vivamus magna. Cras in mi at felis aliquet congue. Ut a est eget ligula molestie gravida. Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        elit sit amet quam. Vivamus pretium ornare est.</p>
        <p>
        Curabitur massa. Donec eleifend, libero at sagittis mollis, tellus est malesuada tellus, at luctus turpis
        </p>
    </blockquote>
  
    <h3>Header Level 3</h3>
  
    <ul>
      <li>Lorem ipsum dolor sit amet, consectetuer adipiscing elit.</li>
      <li>Aliquam tincidunt mauris eu risus.</li>
    </ul>
  </div>
  <script src="shareText.js"></script>
</body>
</html>

window.open lets you open the twitter page(https://twitter.com/intent/tweet) where you can share the selected text and also url.