How to create Object with nested Objects from an Array

Question

I have an array [1, 2, 3] and I want to transfer it to object with nested parent-child objects's series like this :

{ value: 1, rest: { value: 2, rest: { value: 3, rest: null } } 

If I have an array [1, 2, 3, 4] the result will be like this :

{ value: 1, rest: { value: 2, rest: { value: 3, rest: { value:4, rest:null } } 

The best effort of me is this snippet of code :

const arrayToList = (array) => {
 let list = { value: null, rest: null };
 for (let e of array) {
 array.indexOf(e) === 0 && (list.value = e);
 array.indexOf(e) >= 1 && (list.rest = { value: e });
 }
 return list;
};
console.log(arrayToList([1, 2, 3]));

• Boussadjra Brahim: did you see my answer ? if there's something went wrong with it please let me know
• Ala Eddine Menai: Yes. It works well.
• Boussadjra Brahim: Thank you my bro !

Answer 1

You can use reduceRight like so:

let obj = arr.reduceRight((rest, value) => ({ value, rest }), null);

It starts building the object from the inside out; it starts by creating the innermost object and then it uses that object as the rest property for the next outer object and so on until there are no more items in the array.

Demo:

let obj = [1, 2, 3, 4].reduceRight((rest, value) => ({ value, rest }), null);
console.log(obj);

• Ala Eddine Menai: I'd just say: Wonderful! because I hate writing functions with if-else.
• ibrahim mahrir: @MenaiAlaEddine-Aladdin Thanks! The trick here is to start from the last item of the array and building the object from the inside out. Even if you use a simple for loop instead of reduceRight, if you start from the last item, you won't need if-else.
• ibrahim mahrir: @MenaiAlaEddine-Aladdin ... like this jsfiddle.net/gd94npqf which is pretty much exactly what reduceRight is doing

Answer 2

You can create such object by running below recursive function:

let arr = [1, 2, 3, 4];
let transform = (arr, obj) => {
 if(arr.length === 0){
 return obj;
 } else {
 let last = arr[arr.length - 1];
 let newArr = arr.slice(0, arr.length - 1);
 
 return transform(newArr, { value: last, rest: obj || null })
 }
};
console.log(transform(arr));

• Ala Eddine Menai: I want to avoid recursive functions for long-time execution if the array will be big.

Answer 3

Use a recursive function:

let array = [1, 2, 3];
function arrayToL(array) {
 let el = array.splice(0, 1)[0];
 let rtn = {
 value: el
 }
 rtn.rest = (array.length > 0) ? arrayToL(array) : null;
 return rtn;
}
console.log(arrayToL(array));

Answer 4

I suggest another solution using the spread operator and reversing the array and start building object from the array end :

let arr = [1, 2, 4, 5]
let obj = {} //object to be built
arr.slice().reverse().forEach(item => { //i used the slice method 
 //in order to avoid mutating
 //the original variable
 obj = { ...obj,
 ...{
 value: item,
 rest: obj
 }
 };
})
console.log(obj)