Objects and Key-Value Utilities

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JavaScript is a programming language that makes web pages interactive. These examples are for front-end developers, bootcamp students, self-taught coders, and anyone preparing for JS interviews.

Last updated: October 2026 · 102 examples

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Who is this for: Front-end developers, bootcamp students, interview candidates, and self-taught coders building JavaScript skills. Use this when: you need quick reference code, want to practice for interviews, or learn JS concepts hands-on.

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Topics102
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JavaScript Program to Check if a Key Exists in an Object

Use in operator.

Source Code
const o={a:1}; console.log("a" in o);
Expected Output
JavaScript Program to Create Objects in Different Ways
Object literal, constructor, class.
Source Code
const o1={x:1}; function Person(n){this.name=n;} const o2=new Person("Ann"); class Car{constructor(m){this.model=m;}} const o3=new Car("Civic"); console.log(o1,o2,o3);
Expected Output
JavaScript Program to Remove a Property from an Object
Delete a property.
Source Code
const o={a:1,b:2}; delete o.b; console.log(o);
Expected Output
JavaScript Program to Clone a JS Object
Clone using structuredClone.
Source Code
const o={a:1,b:{c:2}}; const c=structuredClone(o); console.log(c);
Expected Output
JavaScript Program to Loop Through an Object
Loop entries.
Source Code
const o={a:1,b:2}; for(const [k,v] of Object.entries(o)){ console.log(k,v); }
Expected Output
JavaScript Program to Merge Property of Two Objects
Merge using spread.
Source Code
const a={x:1}, b={y:2}; const c={...a,...b}; console.log(c);
Expected Output
JavaScript Program to Count the Number of Keys/Properties in an Object
Use Object.keys length.
Source Code
const o={a:1,b:2,c:3}; console.log(Object.keys(o).length);
Expected Output
JavaScript Program to Add Key/Value Pair to an Object
Assign a new key.
Source Code
const o={}; o.name="Alice"; console.log(o);
Expected Output
JavaScript Program to Sort Array of Objects by Property Values
Sort by property.
Source Code
const a=[{n:2},{n:1}]; a.sort((x,y)=>x.n-y.n); console.log(a);
Expected Output
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FAQ
Yes, run them instantly. Copy the code into our online JS compiler or your browser console (F12 → Console). Output uses console.log.
ES6+ (modern JavaScript). All examples work in Chrome, Firefox, Safari, and Edge. Arrow functions, template literals, and destructuring are used where appropriate.
Yes, absolutely. All examples are free to copy, modify, and share. Experimentation is the fastest way to learn JavaScript.
Start with basics, then build up. Begin with Hello World → variables → arithmetic → control flow → functions → strings → arrays → objects.
Learn JavaScript by Practicing Examples
Hands-on practice is the fastest way to understand JavaScript. Each example above focuses on a single concept—from strings, arrays, and objects to math utilities, dates, loops, and functions. Try editing variables, adding conditions, or refactoring logic, then observe the output changes instantly.
Use our tools to deepen your learning: JavaScript Compiler to run snippets, and the JavaScript Tutorial for guided theory and practice.
Beginner-Friendly
Start with variables, operators, and control flow. Build confidence with simple, readable programs.
Practical Patterns
Practice common tasks like formatting strings, manipulating arrays, and working with dates.
Grow Skills
Advance to objects, classes, and asynchronous patterns such as promises and async/await.