Flatten JavaScript objects into a single-depth Object

Last Updated : 19 Aug, 2026

A nested JavaScript object can be flattened into a single-level object by recursively traversing its properties and combining nested keys using a separator such as ..

  • Use typeof to identify nested objects.
  • Recursively process nested objects while preserving their key paths.
  • Keep primitive values and arrays as they are.

Approach: Using Recursion and typeof

The recursive approach checks each property and calls the function again when a nested object is found. The nested keys are combined using . to create a single-level object.

JavaScript 
// Declare an object
let ob = {
    Company: "GeeksforGeeks",
    Address: "Noida",
    contact: +91-999999999,
    mentor: {
        HTML: "GFG",
        CSS: "GFG",
        JavaScript: "GFG"
    }
};

// Declare a flatten function that takes 
// object as parameter and returns the 
// flatten object
const flattenObj = (ob) => {

    // The object which contains the
    // final result
    let result = {};

    // loop through the object "ob"
    for (const i in ob) {

        // We check the type of the i using
        // typeof() function and recursively
        // call the function again
        if ((typeof ob[i]) === 'object' && !Array.isArray(ob[i])) {
            const temp = flattenObj(ob[i]);
            for (const j in temp) {

                // Store temp in result
                result[i + '.' + j] = temp[j];
            }
        }

        // Else store ob[i] in result directly
        else {
            result[i] = ob[i];
        }
    }
    return result;
};

console.log(flattenObj(ob));

Output
{
  Company: 'GeeksforGeeks',
  Address: 'Noida',
  contact: -999999908,
  'mentor.HTML': 'GFG',
  'mentor.CSS': 'GFG',
  'mentor.JavaScript': 'GFG'
}
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