Get width of a column in bootstrap grid

Question

How do I get the width of a column in a bootstrap grid? I can't get the code to return a value like the number of px. Also, I expect the number to change when I resize my browser.

 var width = document.getElementById("answer"); var unit = document.getElementsByClassName("col-3"); var x = unit.width; width.textContent = x; 

 .col-3 { height:100px; } #a { background: red; } #b { background:blue; } 

 <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/css/bootstrap.min.css" integrity="sha384-Zug+QiDoJOrZ5t4lssLdxGhVrurbmBWopoEl+M6BdEfwnCJZtKxi1KgxUyJq13dy" crossorigin="anonymous"> <div class="container-fluid"> <div class="row"> <div class="col-3" id="a">Width:<span id="answer">0</span></div> <div class="col-3" id="b"></div> <div class="col-3"></div> <div class="col-3"></div> </div> </div> <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/js/bootstrap.min.js" integrity="sha384-a5N7Y/aK3qNeh15eJKGWxsqtnX/wWdSZSKp+81YjTmS15nvnvxKHuzaWwXHDli+4" crossorigin="anonymous"></script> 

Answer 1

You need get first-child col-3 in row, because col-3 after first-child width:0

 $(document).ready(function(){ var unit = $(".col-3:first-child").width(); var width = $("#answer").text(unit); }); 

 .col-3 { height:100px; } #a { background: red; } #b { background:blue; } 

 <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/css/bootstrap.min.css" integrity="sha384-Zug+QiDoJOrZ5t4lssLdxGhVrurbmBWopoEl+M6BdEfwnCJZtKxi1KgxUyJq13dy" crossorigin="anonymous"> <div class="container-fluid"> <div class="row"> <div class="col-3" id="a">Width:<span id="answer">0</span></div> <div class="col-3" id="b"></div> <div class="col-3"></div> <div class="col-3"></div> </div> </div> <script src="https://code.jquery.com/jquery-3.2.1.slim.min.js" integrity="sha384-KJ3o2DKtIkvYIK3UENzmM7KCkRr/rE9/Qpg6aAZGJwFDMVNA/GpGFF93hXpG5KkN" crossorigin="anonymous"></script> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js" integrity="sha384-ApNbgh9B+Y1QKtv3Rn7W3mgPxhU9K/ScQsAP7hUibX39j7fakFPskvXusvfa0b4Q" crossorigin="anonymous"></script> <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta.3/js/bootstrap.min.js" integrity="sha384-a5N7Y/aK3qNeh15eJKGWxsqtnX/wWdSZSKp+81YjTmS15nvnvxKHuzaWwXHDli+4" crossorigin="anonymous"></script>