console.log( 1 - 0.8 ); //输出 0.19999999999999996 
console.log( 6 * 0.7 ); //输出 4.199999999999999 
console.log( 0.1 + 0.2 ); //输出 0.30000000000000004 
console.log( 0.1 + 0.7 ); //输出 0.7999999999999999 
console.log( 1.2 / 0.2 ); //输出 5.999999999999999 

//加 
function floatAdd(arg1,arg2){ 
  var r1,r2,m; 
  try{r1=arg1.toString().split(".")[1].length}catch(e){r1=0} 
  try{r2=arg2.toString().split(".")[1].length}catch(e){r2=0} 
  m=Math.pow(10,Math.max(r1,r2)); 
  return (arg1*m+arg2*m)/m; 
} 
  
//减 
function floatSub(arg1,arg2){ 
 var r1,r2,m,n; 
 try{r1=arg1.toString().split(".")[1].length}catch(e){r1=0} 
 try{r2=arg2.toString().split(".")[1].length}catch(e){r2=0} 
 m=Math.pow(10,Math.max(r1,r2)); 
 //动态控制精度长度 
 n=(r1>=r2)".")[1].length}catch(e){} 
 try{m+=s2.split(".")[1].length}catch(e){} 
 return Number(s1.replace(".",""))*Number(s2.replace(".",""))/Math.pow(10,m); 
} 
  
  
//除 
function floatDiv(arg1,arg2){ 
  var t1=0,t2=0,r1,r2; 
  try{t1=arg1.toString().split(".")[1].length}catch(e){} 
  try{t2=arg2.toString().split(".")[1].length}catch(e){} 
   
  r1=Number(arg1.toString().replace(".","")); 
 
  r2=Number(arg2.toString().replace(".","")); 
  return (r1/r2)*Math.pow(10,t2-t1); 
}