matchesSelector()方法

let result = element.matches(selectorString);

• result 的值为 true 或 false.
• selectorString 是个css选择器字符串.

• if (!Element.prototype.matches) {
      Element.prototype.matches = 
          Element.prototype.matchesSelector || 
          Element.prototype.mozMatchesSelector ||
          Element.prototype.msMatchesSelector || 
          Element.prototype.oMatchesSelector || 
          Element.prototype.webkitMatchesSelector ||
          function(s) {
              var matches = (this.document || this.ownerDocument).querySelectorAll(s),
                  i = matches.length;
              while (--i >= 0 && matches.item(i) !== this) {}
              return i > -1;            
          };
  }