How to get header from cards or similar to have the same height with flex box?

Question

There are basically 2 ways to accomplish this, the CSS way,

CSS – How to have children in different parents the same height?

and the script way, here using jQuery.

The first script sample shows how to set equal height on all items.

Second sample set equal height per row, and the way to make that work is to check the item’s top value (it changes for a new row) and set the height for each processed range/row.

I also added a couple of optimizations, preload items and so it won’t process them if there is only 1 item or column.

Updated codepen 1

Stack snippet 1

(function ($) {

  // preload object array to gain performance
  var $headers = $('.header')
  
  // run at resize
  $( window ).resize(function() {
    $.fn.setHeaderHeight(0);   
  });  

  $.fn.setHeaderHeight = function(height) {

    // reset to auto or else we can't check height
    $($headers).css({ 'height': 'auto' });
    
    // get highest value
    $($headers).each(function(i, obj) {    
      height = Math.max(height, $(obj).outerHeight()) 
    });

    // set the height
    $($headers).css({ 'height': height + 'px' });    
  }

  // run at load
  $.fn.setHeaderHeight(0);
  
}(jQuery));

body{
  padding: 20px;
}

.item{
  height: 100%;
  padding-right: 20px;
  padding-top: 20px;
  display: flex;
  flex-direction: column
}

.header{
  background-color: cornflowerblue;
}

.content{
  background-color: salmon;
  flex-grow: 1;
}

.mycontainer{
  max-width: 500px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.css" rel="stylesheet"/>

<div class="row mycontainer">
  <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
      <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
      </div>
  </div>
  <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala some content lala some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
      <div class="item">
       <div class="header">oh no this header wraps</div>
        <div class="content">some content lala </div>
      </div>
  </div>
</div>

Updated codepen 2

Stack snippet 2

(function ($) {
  //  preload object array to gain performance
  var $headers = $('.header')

  // only do this if there is more than 1 item
  if ($headers.length < 2) { return; }
    
  //  run at resize
  $( window ).resize(function() {
    $.fn.setHeaderHeight(0,0);   
  });

  $.fn.setHeaderHeight = function(height, idx) {
    // reset to auto or else we can't check height
    $($headers).css({ 'height': 'auto' });
     
    $($headers).each(function(i, obj) {    

      // only continue if there is more than 1 column
      if ($($headers).eq(0).offset().top !== $($headers).eq(1).offset().top  ) {
        return false;
      }
      
      // get highest value
      height = Math.max(height, $(obj).outerHeight()) 
      
      // did top value changed or are we at last item
      if (i != 0 && $($headers).eq(i - 1).offset().top != $(obj).offset().top) {

        // set height for row
        $($headers).slice(idx, i).css({ 'height': height + 'px' });
        
        // reset height and startIndex
        height = 0;
        idx = i;
      } else if ($headers.length - 1 == i) {
        
        // last row
        $($headers).slice(idx, i + 1).css({ 'height': height + 'px' });   
      }

    });        
  }
  
  //  run at load
  $.fn.setHeaderHeight(0,0);

}(jQuery));

body{
  padding: 20px;
}

.item{
  height: 100%;
  padding-right: 20px;
  padding-top: 20px;
  display: flex;
  flex-direction: column
}

.header{
  background-color: cornflowerblue;
}

.content{
  background-color: salmon;
  flex-grow: 1;
}

.mycontainer{
  max-width: 500px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.css" rel="stylesheet"/>

<div class="row mycontainer">
  <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
      <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
      </div>
  </div>
  <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala some content lala some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
      <div class="item">
       <div class="header">oh no this header wraps</div>
        <div class="content">some content lala </div>
      </div>
  </div>
</div>

As some prefer plain javascript, I updated with such sample as well (setting equal height on all items), which apply/add a class dynamically, with the computed height value.

Stack snippet

(function(d,t,h) {
  /*  preload some variables  */
  h = (d.head || d.getElementsByTagName('head')[0]);
  var items = d.querySelectorAll('.header');
  
  function resized() {
    var heights = [], i = 0, css;
    /*  delete set style so we get proper value  */
    removeElement('head_dynamic_css');
    for (i = 0; i < items.length; i++) {
      heights.push(parseFloat(window.getComputedStyle(items[i], null).getPropertyValue("height")));
    }
    css = ".header { height: " + Math.max.apply(null, heights) + "px; }";
    /*  create and add style with height  */
    var s = d.createElement('style');
    s.type="text/css";
    s.id = 'head_dynamic_css';
    if (s.styleSheet) {
      s.styleSheet.cssText = css
    } else {
      s.appendChild(d.createTextNode(css));
    }
    h.appendChild(s);
  }

  window.addEventListener("load", resized, false);
  window.addEventListener("resize", resizer, false);
  function resizer() {
    if (!t) {
      t = setTimeout(function() {
        t = null;
        resized();
       }, 66);
    }
  }
  function removeElement(el) {
    var el = document.getElementById(el);
    if (el) {
      el.parentElement.removeChild(el);
    }
  }
}(document,null));

body {
  padding: 20px;
}

.item {
  height: 100%;
  padding-right: 20px;
  padding-top: 20px;
  display: flex;
  flex-direction: column
}

.header {
  background-color: cornflowerblue;
}

.content {
  background-color: salmon;
  flex-grow: 1;
}

.mycontainer {
  max-width: 500px;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.css" rel="stylesheet"/>

<div class="row mycontainer">
  <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
      <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
      </div>
  </div>
  <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
    <div class="item">
       <div class="header">bippo</div>
        <div class="content">some content lala some content lala some content lala </div>
    </div>
  </div>
    <div class="col-12 col-md-4 col-lg-3">
      <div class="item">
       <div class="header">oh no this header wraps</div>
        <div class="content">some content lala </div>
      </div>
  </div>
</div>

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