How to create generic CSS class with input paramet

Question

I am showing list of items on UI. Those items have attribute as tLevel. Depending on tLevel value I want to create tree structure.

Something like this

item1                   tLevel=0
    item2               tLevel=1
        item3           tLevel=2    
    item4               tLevel=1
        item5           tLevel=2
            item6       tLevel=3    
            item7       tLevel=3
            item8       tLevel=3
item9                   tLevel=0
    item10              tLevel=1
    item11              tLevel=1

HTML template

<div class="treeLevelCSS(' + tLevel + ')" />

CSS should be something like

.treeLevelCSS(tLevel){
    "margin-left: " + (tLevel * 15) + "px"
}

I am not sure what I have written above in HTML and CSS is right, but just to give an idea of what I want to achieve here.

Answer 1

If you're using Less, what you need in a simplest case is a mixin and selector "interpolation", e.g.:

.treeLevel(0);
.treeLevel(1);
.treeLevel(2);
.treeLevel(3);

.treeLevel(@level) {
    .treeLevelCSS@{level} {
        margin-left: @level * 15px;
    }
}

Then, depending on your needs, get it further improved with other stuff. For example using loops to reduce repetition and/or possibility to generate an arbitrary number of class. See native Less loops and/or a syntactic sugar goodies for those like .for:

@import "for";

.tree-level- {
    // generate 8 level classes:
    .for(0, 7); .-each(@i) {
        &@{i} {
            margin-left: 15px * @i;
        }
    }
}

Codepen Demo for above (slightly modified) snippet.

Answer 2

If possible it might be beneficial to use nested lists here, with each level just having padding applied to it.

For example:

<ul>
  <li>1</li>
  <li>
    <ul>
      <li>2</li>
      <li>
        <ul>
          <li>3</li>
        </ul>
      </li>
      <li>2</li>
    </ul>
  </li>
  <li>1</li>
</ul>

and...

li {
  list-style:none;
}
ul ul {
  padding-left:20px;
}

Should do the job, demo: http://codepen.io/merlinmason/pen/vORaVB