SOURCE

function numFormat(num) {
  var NUM,
      rules; 
  if(num === undefined ||num === null)return '0';
	NUM = Number(num);
  if ( NUM < 10000 )return NUM;
  rules = [
    {
      //大于一万
      match: function(param){
        return param >= 10000 && param < 10000000;
      },
      action: function(param){
        param = ( Math.round( param / 1000 ) ) / 10 + '万';
        return param;
      }
    },
    {
      //大于1000万
      match: function(param){
        return param >= 10000000 && param < 1000000000;
      },
      action: function(param){
        param = ( Math.round( param / 1000000 ) ) / 10 + '千万';
        return param;
      }
    },
    {
      //大于1亿
      match: function(param){
        return param >= 1000000000;
      },
      action: function(param){
        param = ( Math.round( param / 10000000 ) ) / 10 + '亿';
        return param;
      }
    }
  ]
  
  for ( var i = 0; i < rules.length; i++ ){
    if( rules[i].match(NUM)){
      return rules[i].action(NUM);
    }
  }
}
var num= numFormat(undefined)
console.log(num)