Convert list object into array

Question

I have a list object

{
 value: 5,
 rest: {
 value: 10,
 rest: {
 value: 15,
 rest: null
 }
 }
}

that should be converted into array. I was trying to iterate through the list to take the values and push them into array.

function listToArr(obj){
let arr = []
 for (let val in object){
 arr.push(Object.values(val))
 }
 return arr
}

But I am getting [ [ 'v', 'a', 'l', 'u', 'e' ], [ 'r', 'e', 's', 't' ] ]

• hgb123: for..in will iterate through the object's keys, here value and rest, and a string is an array of characters, or object of pairs of index-character, which lead to your unexpeceted result above. what is your expected output in this case?

Answer 1

You'd need to reassign the object inside a loop and access its value property:

console.log(listToArr({ value: 5, rest: { value: 10, rest: { value: 15, rest: null } } }));
function listToArr(obj){
 const arr = [];
 while (obj.rest) {
 arr.push(obj.value);
 obj = obj.rest;
 }
 arr.push(obj.value);
 return arr;
}

Since the keys are static, using Object.values or for..in doesn't accomplish anything.

• Spangle: Nice, however a nitpick would be not to mutate the argument.
• CertainPerformance: The argument is not getting mutated. This would work just fine in React, for example.
• Spangle: Fair enough, I can see use cases for and against this lint rule: eslint.org/docs/rules/no-param-reassign

Answer 2

An ES6 style approach:

let listToArr = (obj) => obj.rest ? [obj.value, ...listToArr(obj.rest)] : [obj.value];
console.log(listToArr({ value: 5, rest: { value: 10, rest: { value: 15, rest: null } } }));

Answer 3

There's a nice recursive solution for this as well. Something like:

let a = {
 value: 5,
 rest: {
 value: 10,
 rest: {
 value: 15,
 rest: null
 }
 }
}
function listToArr(obj, arr){
 arr = arr || [];
 if (!obj) return arr;
 return listToArr(obj.rest, arr.concat(obj.value));
}
console.log(listToArr(a));