If one of those two expressions couldpossibly generate an error condition or a side effect, this could lead to invalidbehavior. Such is the case for our earlier example

The DSL has a weaker control over the program’s flow — we can’t have conditions unless we add a special step

Maybe $$slots like $$props? My use case is that I'd like to wrap a slot's content in an element that applies styling that I'd like absent without the slotted content. Something like this: {#if $$slots.description} <div class="description"> <slot name="description"></slot> </div> {/if}

// require('hammerjs') when in a browser. This is safe because Hammer is only // invoked in componentDidMount, which is not executed on the server. var Hammer = (typeof window !== 'undefined') ? require('hammerjs') : undefined