CODEWITHSUNDEEP
javascriptclosuresfibonacci
winterishere
winterishere

Reputation: 389

Javascript closure in fibonacci series using dynamic programming

I am trying to figure out closure in Javascript.

Trying to calculate fibonacci series using DP. Here my input will be index: Index = 10 And the output: 55 (As per fibonacci seq: 0,1,1,2,3,5,8,13,21,34,55..)

Below version is a working code:

function recursiveDynamicProgramming(){
let cache = {};
//use javascript closure method
return function getFib(n){
//var getFib = function(n){ : When i assign function to this variable. I am getting undefined error. Although it has return value :(
    if(n in cache){//if(cache[n])
        return cache[n];
    } else{
        if(n < 2){
            return n;
        }else{
            cache[n] = getFib(n - 2) + getFib(n - 1);
            return cache[n];
        }
    }
}
}  
const dynamicProdFib = recursiveDynamicProgramming();
console.log(dynamicProdFib(10)); //Output = 55, Input = 10
//console.log(dynamicProdFib.getFib(10)); //This should give me the same result as the variable getFib is defined in the program.

So here if you can refer the commented code where

//var getFib = function(n){ : When i assign function to this variable. I am getting undefined error. 
 Although it has return value //Or we can use this.getFib = function(n)

But when i try to call this method I am getting undefined error. Which simply means my function is not returning a value. But i am returning value inside this function. I am not sure where i am making mistake.

We have several examples of this question but i am not able to wrap my head around this. Please pardon me for this. Thank you for the help :)

UPDATE: Thanks @Bergi for pointing my silly mistake.

In my case i am trying to call the output like :

dynamicProdFib.getFib(10)

so i have to put the output in an object:

  return {getFib};

Or simply call the output as:

return dynamicProdFib(10)

Hope this is helpful :)

Upvotes: 0

Views: 225

Answers (1)

Bergi
Bergi

Reputation: 664777

That you are returning inside the getFib function is not enough, the part you were missing is that you also need to return the getFib function from recursiveDynamicProgramming. It might help to introduce a helper variable for that though:

function recursiveDynamicProgramming() {
    let cache = {};
    var getFib = function(n) { // or just "function getFib(n) {"
        …
    };
    return getFib;
//  ^^^^^^^^^^^^^^
}

Upvotes: 1

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