JS:使用reduce实现map

方法一

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

方法二

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