Checking if a nested object contains only single key-value pair in javascript

Question

I want to check if a deeply nested object consists of single key-value pair, if it does, it should return true else false.

For e.g., I want the below code to return true,

var test = {
 level1:
 {
 level2:
 {
 level3:'level3'
 }
 } 
 };

And the below code to return false,

var test2 = {
 level1: {
 level2: {'a': '1', 'b': 2},
 level3: {'a': '2', 'c': 4}
 }
 };

Also, the below code should return true,

var test3 = 
{
 level1: {
 level2: {
 level3: {
 level4: {
 1: "1",
 2: "2",
 3: "3",
 4: "4"
 }
 }
 }
 }
}

I made the following program for it, but it doesn't work,

function checkNested(obj) {
 if(typeof(obj) === 'object') {
 if(Object.keys(obj).length === 1) {
 var key = Object.keys(obj);
 checkNested(obj[key])
 } else { 
 return(false);
 }
 }
 return(true);
}

Could someone please suggest me how can I achieve it?

Answer 1

With var key = Object.keys(obj);, key becomes an array (containing the one key), so obj[key] doesn't make sense. You might destructure the [key] instead:

const [key] = Object.keys(obj);
return checkNested(obj[key])

(make sure to return the recursive call)

Or, even better, use Object.values, since you don't actually care about the keys:

var test = {
 level1: {
 level2: {
 level3: 'level3'
 }
 }
};
var test2 = {
 level1: {
 level2: 'level2',
 level3: 'level3'
 }
};
function checkNested(obj) {
 if (typeof(obj) === 'object') {
 const values = Object.values(obj);
 if (values.length !== 1) {
 return false;
 }
 return checkNested(values[0]);
 }
 return true;
}
console.log(checkNested(test));
console.log(checkNested(test2));

• Frosted Cupcake: Your code is returning false for the below code, var test3 = { level1: { level2: { level3: { level4: { 1: "1", 2: "2", 3: "3", 4: "4" } } } } }
• CertainPerformance: Yep, because it has more than one nested key-value pair.
• Frosted Cupcake: Hi, I updated my question, I want the code to return true even for test3
• CertainPerformance: It does return false for test3. (as your first comment noted)
• Frosted Cupcake: My bad, I want it to return true even in such cases as test3