Javascript: HackerRank function within a function is not a function

Question

This is one of those job interview tests on HackerRank that I am embarrassed to say I didn't complete within the allotted 20 minutes, and it's driving me nuts. Basically, you're given the following:

function myList() { // write code here } function main() { // You can't edit this function. This is just pseudo, from what I can remember const obj = myList(); if (operation === "add") obj.add(item); else if (operation === "remove") obj.remove(item); else obj.getList(); // Some more stuff here }

So my first train of thought was to write the following inside myList():

let objList = []; function add(item) { objList.add(item) } // etc., etc. return {add, remove, getList};

Needless to say, the above didn't work, with the error: obj.add is not a function, in the main function.

I tried experimenting with this and the returns (only returning add, with or without {}), but didn't really get anywhere. What could I have done to get this working?

bajro · Accepted Answer · 2022-02-11 09:01:00Z

As the answer from Attersson already suggested, you could use a closure inside the myList function. This would allow to only expose the three methods add, remove and getList while the original list cannot be accessed. Here is an example:

function myList() { return (() => { const obj = {itemList: []} const add = (item) => obj.itemList.push(item) const remove = (item) => obj.itemList = obj.itemList.filter(i => i !== item) const getList = () => obj.itemList return {add, remove, getList} })() }

Attersson · Accepted Answer · 2022-02-11 08:30:55Z

For obj, inside myList() you could have run a closure, that is a self invoking function returning, in this case, an object with your k:v exports, but with private access to the context of the now expired anonymous caller. With "const add = function" etc statements you can define values for your exports, while the objList goes in the private context.

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