Extract properties from an object in JavaScript

We have to write a JavaScript function, say extract() that extracts properties from an object to another object and then deletes them from the original object.

For example ?

If obj1 and obj2 are two objects, then

obj1 = {color:"red", age:"23", name:"cindy"}
obj2 = extract(obj1, ["color","name"])

After passing through the extract function, they should become like ?

obj1 = { age:23 }
obj2 = {color:"red", name:"cindy"}

Therefore, let's write the code for this function ?

Syntax

const extract = (obj, ...keys) => {
    // Create new object for extracted properties
    // Delete specified keys from original object
    // Return new object with extracted properties
};

Example: Basic Property Extraction

const obj = {
    name: "Rahul",
    job: "Software Engineer",
    age: 23,
    city: "Mumbai",
    hobby: "Reading books"
};

const extract = (obj, ...keys) => {
    const newObject = Object.assign({});
    Object.keys(obj).forEach((key) => {
        if(keys.includes(key)){
            newObject[key] = obj[key];
            delete obj[key];
        };
    });
    return newObject;
};

console.log("Extracted properties:", extract(obj, 'name', 'job', 'hobby'));
console.log("Remaining object:", obj);

Extracted properties: { name: 'Rahul', job: 'Software Engineer', hobby: 'Reading books' }
Remaining object: { age: 23, city: 'Mumbai' }

Example: Extract with Array Parameter

const user = {
    id: 1,
    username: "john_doe",
    email: "john@example.com",
    password: "secret123",
    role: "admin"
};

const extractFromArray = (obj, keysArray) => {
    const extracted = {};
    keysArray.forEach(key => {
        if (key in obj) {
            extracted[key] = obj[key];
            delete obj[key];
        }
    });
    return extracted;
};

const sensitiveData = extractFromArray(user, ["password", "email"]);
console.log("Sensitive data:", sensitiveData);
console.log("Safe user object:", user);

Sensitive data: { password: 'secret123', email: 'john@example.com' }
Safe user object: { id: 1, username: 'john_doe', role: 'admin' }

Alternative Method: Using Object Destructuring

const product = {
    id: 101,
    name: "Laptop",
    price: 999,
    category: "Electronics",
    inStock: true
};

const extractUsingDestructuring = (obj, keys) => {
    const extracted = {};
    const remaining = { ...obj };
    
    keys.forEach(key => {
        if (key in remaining) {
            extracted[key] = remaining[key];
            delete remaining[key];
        }
    });
    
    // Update original object
    Object.keys(obj).forEach(key => delete obj[key]);
    Object.assign(obj, remaining);
    
    return extracted;
};

const metadata = extractUsingDestructuring(product, ["id", "category"]);
console.log("Extracted metadata:", metadata);
console.log("Product details:", product);

Extracted metadata: { id: 101, category: 'Electronics' }
Product details: { name: 'Laptop', price: 999, inStock: true }

Comparison

Key Points

The extract function is useful for:

• Separating sensitive data from public object properties
• Creating specialized objects from larger data structures
• Data transformation and cleanup operations
• Implementing object property filtering

Conclusion

The extract function provides a clean way to move properties between objects while modifying the original. Use rest parameters for simple cases or array parameters for dynamic property extraction.