difference btw comibineReducers with map and reduce ?

combineReducers.js

const combineReducers = (reducers)=>{
	return (state = {} , action)=>{
		Object.keys(reducers).reduce(function( nextState , key ){
			nextState[key] = reducers[key](state[key] , action);
			return nextState;
		} , {})
	}
} 


const combineReducers = (reducers)=>{
	return (state , action){
		const nextState = {}
		Object.keys(reducers).map((state , action)=>{
			nextState[key] = state[key](state[key] , action)	
		})
		return nextState
	}
}