code: function $$(selector, context){
  
  	if ( typeof selector == 'object' ) {
  		return new Dom(selector);
  	}
  
  	let doc = context || document;
  	let byId = selector.substring(0, 1) == '#';
  	let qs;
  
  
  	// 按ID查询，有一个便是
  	if ( byId ) {
  		qs = document.getElementById(selector.substring(1));
  		return new Dom(qs ? [qs] : []);
  	}
  
  	if ( doc instanceof Dom ) {
  		let ary = [], qs;
  		if ( byId ) {
  			for ( let i=0; i<doc.length; i++ ) {
  				qs = doc[i].querySelectorAll(selector);
  				for ( let j=0; j<qs.length; j++ ) {
  					ary.push(qs[j]); // 按class查询，有一个算一个
  				}
  			}
  		}
  		return new Dom(ary);
  	} 
  
  	return new Dom(doc.querySelectorAll(selector));
  }
docs: 选择器 $$('.xxxx')