Truncates texts that would otherwise be hidden due to overflow: hidden and adds an ellipses (…). This only works for multi-line text and not single-line text since any browser that Dart targets should support the text-overflow CSS property that has built-in support for single-line auto-ellipses.

ellipses.dart

void ellipses(Element el){  
  
  final tempElement = el.clone(true);
  if(el.getComputedStyle().overflow == 'hidden'){    
    tempElement.style.position = 'absolute';
    tempElement.style.overflow = 'visible';
    tempElement.style.width = '${el.clientWidth}px';
    tempElement.style.height = 'auto';
    tempElement.style.maxHeight = 'none';
    el.insertAdjacentElement('afterEnd', tempElement);
    
    final desiredHeight = el.clientHeight;
    final allNodes = new List<Node>();
    
    for(final node in tempElement.nodes){
      addAllNodes(node, allNodes);
    }

    while(tempElement.clientHeight > desiredHeight){
      for(int i = allNodes.length - 1; i >=0; i--){
        final curNode = allNodes[i];
        
        if(curNode.text.trim().isEmpty){
          curNode.remove();
          continue;
        }
        
        var curText = curNode.text.trim();
        
        while(curText.length > 0){                   
          final nextCutoff = curNode.text.lastIndexOf(' ');
          
          if(nextCutoff == -1){
            curNode.remove();
            break;
          }
          
          final nextCutoffText = curNode.text.substring(0, nextCutoff);
          curText = '${nextCutoffText}…';
          curNode.text = curText;
          el.innerHtml = tempElement.innerHtml;
          
          if(tempElement.clientHeight <= desiredHeight){
            tempElement.remove();
            return;
          }
        }
      }
    }
    tempElement.remove();
  }
}

void addAllNodes(Node curNode, List<Node> nodes){
  nodes.add(curNode);
  for(final node in curNode.nodes){
    addAllNodes(node, nodes);
  }
}