Javascript Object Interview Questions
Key Topics to Cover in Javascript Object Interview Questions
Javascript Object Interview Questions are commonly asked during interviews to assess a candidate's understanding of objects in Javascript. These questions can cover a range of topics such as creating objects, accessing object properties and methods, using constructors and prototypes, and manipulating objects. Interviewers also look for a thorough understanding of object-oriented programming concepts like encapsulation, inheritance, and polymorphism. Candidates are expected to demonstrate their ability to work with objects efficiently, troubleshoot common errors, and optimize object performance. Familiarity with popular object manipulation methods and ES6 features like classes and arrow functions is also desirable.
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1 - What is an object in JavaScript?
An object in JavaScript is a complex data type that allows us to store multiple values and functions together as a single entity. It is created using curly braces {} and can hold various properties and methods. Objects are useful for organizing and storing different types of data in a structured way.
2) How do you access the properties and methods of an object?
To access the properties and methods of an object, we use dot notation (object.property) or bracket notation (object['property']). Dot notation is commonly used when we know the property name at the time of writing the code, while bracket notation is useful when the property name is stored in a variable or consists of special characters.
3) What is the difference between objects and arrays?
Arrays are a special type of object in JavaScript that store a list of values in a specific order. Objects, on the other hand, can store both named properties and values. Arrays are accessed using their numerical index, whereas objects are accessed using their key or property name. Additionally, different arrays can have the same values, while objects must have unique property names.
4) How do you check if a property exists in an object?
We can use the “in” operator to check if an object has a specific property. For example, “property” in object will return true if the object has a property named “property”. Alternatively, we can also use the hasOwnProperty() method, which returns true if the property is a direct property of the object and not inherited from its prototype.
5) What are constructor functions?
Constructor functions are used to create objects in JavaScript. They act as a blueprint for creating multiple objects with the same structure and properties. When the constructor function is called with the “new” keyword, it creates a new object and assigns its properties and methods using the “this” keyword.
6) How do you add or remove properties from an object?
To add a new property to an existing object, we can simply assign a value to it using either dot or bracket notation. For example, object.newProperty = value or object['newProperty'] = value. To remove an existing property, we can use the delete operator delete object.property. However, deleting a property will not alter the object's prototype chain.
7) What is object destructuring in JavaScript?
Object destructuring is a way of extracting properties from an object and assigning them to individual variables. It allows us to access multiple properties at once and can also be used to set default values for properties in case they are undefined.
8) How do you create a copy of an object?
We can use the Object.assign() method to create a shallow copy of an object. This means that any nested objects or arrays within the original object will still be referenced in the new object. To create a deep copy, we can use the JSON.parse() and JSON.stringify() methods, which will create a new object with all its properties and values copied.
9) How do you define a method in an object?
Methods are functions that are assigned as values to properties in an object. To define a method, we can simply assign a function to a property in the object using either dot or bracket notation. We can then call the method using dot notation, passing in any required arguments.
10) What is object prototype in JavaScript?
In JavaScript, objects have an internal prototype property that allows them to inherit properties and methods from other objects. When we attempt to access a property or method in an object, JavaScript will first look for it in the object's own properties and then search its prototype object and continue up the prototype chain until the property is found or returns undefined.
11) How do you prevent modifications to an object?
We can use Object.defineProperty() or Object.defineProperties() to set properties as read only, which will prevent any changes to their values. We can also use Object.freeze() to make an entire object read only, including its properties and values.
12) What is the difference between “==” and “===” in JavaScript?
“==” is an equality operator that compares the values without considering the data type. On the other hand, “===” is a strict equality operator that compares both the value and data type. For example, 1 == ‘1’ will return true, but 1 === ‘1’ will return false.
13) How do you create an empty object?
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We can create an empty object by using the object constructor var obj = new Object(). We can also create an object literal with curly braces {} or use the “null” keyword to assign null to an object.
14) Can you add functions to an object?
Yes, we can add functions to an object as properties, which are known as methods. Methods can be called using dot notation and have access to the object's properties and other methods.
15) What is the “this” keyword in JavaScript?
The “this” keyword refers to the current object within a function or method. It is a way to access and operate on the properties and methods within an object and can change based on how the function or method is called.
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