JavaScript - removing undefined fields from object

Quick solution (ES6+):

const newObject = Object.fromEntries(Object.entries(myObject).filter(([_, value]) => value != null));

Reusable arrow function

// ONLINE-RUNNER:browser;

const removeBlank = (inputObject) => {
    return Object.fromEntries(
        Object.entries(inputObject).filter(([_, value]) => value != null)
    );
}


// Usage example:

const myObject = { a: 1, b: '', c: undefined, d: null };

const newObject = removeBlank(myObject);

console.log(JSON.stringify(newObject)); // { a: 1, b: '' }

Explanation:

To remove properties that are undefined or null we used the following methods:

• Object.entries() - to get array of a given object's properties ([key, value] pairs),
• filter() - to remove properties that values are null or undefined,
• Object.fromEntries() - to create a new result object from filtered [key, value] pairs.

Recursion to remove properties from nested objects

// ONLINE-RUNNER:browser;

const removeBlank = (inputObject) => {
    return Object.fromEntries(
        Object.entries(inputObject)
            .filter(([_, value]) => value != null)
            .map(([key, value]) => [
                key,
                value === Object(value) ? removeBlank(value) : value,
            ])
    );
};


// Usage example:

const myObject = {
    a: 1,
    b: { b1: undefined },
    c: { c1: null },
};

const newObject = removeBlank(myObject);

console.log(JSON.stringify(newObject, null, 4)); // { a: 1, b: {}, c: {} }

References

1. Object.entries() - JavaScript | MDN
2. Object.fromEntries() - JavaScript | MDN
3. Array.prototype.filter() - JavaScript | MDN
4. Array.prototype.map() - JavaScript | MDN