方法一

  1. let _map=function(a,f){
  2.   return a.reduce((sum,value,idx,a)=>{
  3.     sum.push(f(value,idx,a));
  4.     return sum;
  5.   },[]);
  6. }
  7. let a=[1,2,3];
  8. let b=_map(a,value=>value*value);
  9. console.log('rlt:',b);

方法二

  1. Array.prototype._map=function(f,thisArg){
  2.   let self = this || thisArg;
  3.   console.log(thisArg);
  4.   return self.reduce((sum,value,idx,self)=>{
  5.     sum.push(f.bind(self)(value,idx,self));
  6.     return sum;
  7.   },[]);
  8. }
  10. let a=[1,2,3];
  11. let b=a._map(value=>value*value);
  12. console.log('rlt:',b);