[Decode]

<input id="inp" type="checkbox" />
<label for="inp">Bla-bla</label>

<script>
	var inpElem = document.body.children[0],
	    label = inpElem.nextElementSibling;

	inpElem.onclick = function() {
		label.checked = true;
	};

	inpElem.click();
</script>