Manually Traverse a DOM Tree Using jQuery

Example DOM Tree
Image via Wikipedia

jQuery does a wonderful job of traversing the DOM tree, so you might ask why you would like to do this yourself?
I recently encountered a requirement to count the maximum ‘depth’ of a DOM tree. I.e. find the level of the deepest nested element. So, I managed to knock this up in a few minutes:

function Recurse($item, depth) {
    $item.each(function() {
        depth.count++;
        if (depth.count > depth.max) {
            depth.max = depth.count;
        }
        Recurse($(this).children(), depth);
    });
    depth.count--;
    return depth.max;
}

$(document).ready(function() {
    alert(Recurse($("body"), { count: 0, max:0 }));
}

A few points to note about this

  • depth is an object with two members, count and max. We want to keep a count of the current and maximum depth, but want to avoid global variables (it’s better practice, and makes the solution more self-contained).
  • JavaScript doesn’t allow us to pass variables by reference. Using the variables within the passed depth object means we can pass values to lower levels of recursion.
  • We must pass an object in our first call. Technically the function can be improved by including a check for this.
  • The function returns depth.max. Although the return value doesn’t matter when the function is called recursively, its useful for passing our intended value out to the original calling function.

You can test this out on JsFiddle: http://jsfiddle.net/RqHzf/

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