Given a function that returns me “[prop1][prop2][prop3]” for a nested javascript object, how do I get the value of object[prop1][prop2][prop3]? [duplicate]

Question

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I am writing a function to convert array to List using Javascript.

If the input array is as below:

let inputArray = [1,2,3]

The output object should be like the below:

let outputList = { 
    value: 1, 
    rest: {
        value: 2,
        rest: {
            value : 3,
            rest: null } } }

I have the below function that accepts a nested object as its parameter and returns a string that represents where in the object, the property is null:

function getLastValue(object) {
   let s = '';
   if (object.rest) {
     return s += '[rest]' + getLastValue(object.rest);
   } else {
     return s;
}

And the below function that converts an array to a list:

var list = {value: '', rest: null};

function constructList(arr) {
    for (let prop of arr) {
        let lastValue = getLastValue(list);
        `${list}${lastValue}`.value = prop;
        `${list}${lastValue}`.rest = null;
    }
    return list;
}

The constructList function fails to work as ${list}${lastValue} is a string. I need to convert the above from

'list[rest][rest]' 

to

list[rest][rest]

Any help is appreciated!

Answer 1

This would be a great place to use reduceRight - construct the innermost object first, and have it be the new value of the accumulator, which is assigned to the next innermost object's rest property, and so on:

 const constructList = arr => arr.reduceRight( (rest, value) => ({ value, rest }), null ); console.log( constructList([1, 2, 3]) ); 

To fix your original code, rather than constructing a string that attempts to refer to the nested object, iterate through the nested structure to find the innermost rest property instead, and return the object that doesn't contain a truthy rest property:

 function getLastValue(obj) { while (true) { if (!obj.rest) return obj; obj = obj.rest; } } var list = { value: '', rest: null }; function constructList(arr) { for (let prop of arr) { const nestedObj = getLastValue(list); nestedObj.value = prop; nestedObj.rest = {}; } getLastValue(list).rest = null; return list; } console.log( constructList([1, 2, 3]) );