jQuery.support 实现

jQuery.support

/**
 * Support testing using an element
 * @param {Function} fn Passed the created div and expects a boolean result
 */
function assert( fn ) {
	var div = document.createElement("div");

	try {
		return !!fn( div );
	} catch (e) {
		return false;
	} finally {
		// Remove from its parent by default
		if ( div.parentNode ) {
			div.parentNode.removeChild( div );
		}
		// release memory in IE
		div = null;
	}
}
// Check if getElementsByClassName can be trusted
	support.getElementsByClassName = assert(function( div ) {
		div.innerHTML = "<div class='a'></div><div class='a i'></div>";

		// Support: Safari<4
		// Catch class over-caching
		div.firstChild.className = "i";
		// Support: Opera<10
		// Catch gEBCN failure to find non-leading classes
		return div.getElementsByClassName("i").length === 2;
	});