Question

I’m writing an assert function. How do I cache #assert if it doesn’t exist yet?

function assert( outcome, description ) {
   if (!$('#assert').length) {
      $('body').append('<ul id="assert"></ul>');
   }
   $('#assert').append('<li class="' + (outcome ? 'hide' : 'alert-danger') + '">' + description + '</li>');
}

Answer 1

I’d do it like this…

function assert( outcome, description ) {
    var assrt = $('#assert');
    if (!assrt || !assrt.length) {
        assrt = $('<ul>',{id:"assert"}).appendTo('body');
    }
    assrt.append('<li>', {className:outcome ? 'hide' : 'alert-danger', text:description});
}

---

Or if the assert element is meant to be used by subsequent invocations, I’d probably use a closure to maintain a reference between calls…

var assert = (function() {
    var assrt = $('#assert');

    return function( outcome, description )
        if (!assrt || !assrt.length) {
            assrt = $('<ul>',{id:"assert"}).appendTo('body');
        }
        assrt.append('<li>', {className:outcome ? 'hide' : 'alert-danger', text:description});
    };
}());

---

You could expand on this by returning several functions…

var assert = (function() {
    var assrt = $('#assert');

    function verify_assert_container() {
        if (!assrt || !assrt.length) {
            assrt = $('<ul>',{id:"assert"}).appendTo('body');
        }
    }

    return {
        add: function( outcome, description )
            verify_assert_container();
            assrt.append('<li>', {className:outcome ? 'hide' : 'alert-danger', text:description});
        },
        empty: function() {
            verify_assert_container();
            assrt.empty();
        },
        sort: function() {
            verify_assert_container();
            // use sorting algorithm to reorder the LI elements
        },
        destroy: function() {
            if (assrt) {
                assrt.remove();
                assrt = null;
            }
        }
    };
}());

and use it like this…

assert.add('foo', 'bar');
assert.empty();
assert.destroy();