//取整 parseInt(a,10); //Before Math.floor(a); //Before a>>0; //Before ~~a; //After a|0; //After //四舍五入 Math.round(a); //Before a+.5|0; //After //内置值 undefined; //Before void 0; //After, 快 0[0]; //After, 略慢 //内置值 Infinity; 1/0; //布尔值短写法 true; //Before !0; //After //布尔值短写法 false; //Before !1; //After