What is the difference between an “attribute” and a “property” in JavaScript?
Vaibhav KothiaAttribute and property are two terms that are often used interchangeably in JavaScript, but they have slightly different meanings.
An attribute is a characteristic or trait of an element that is not necessarily visible. It usually describes the data associated with the element, such as an id or class. For example, the ‘id’ attribute of a
A property, on the other hand, is a characteristic or trait of an element that is visible. It usually describes the behavior of the element, such as its size or position. For example, the ‘width’ property of a
What is the difference between null and undefined?
Null is a value that indicates the absence of a value. It is often used to indicate an intentional lack of a value, while undefined is a value that indicates that a variable has not been assigned a value.
Example:
Null:
let x = null;
Undefined:
let y;
What is a closure in JavaScript?
A closure is an inner function that has access to the variables and parameters of its outer function, even after the outer function has returned. Closures are a powerful feature of JavaScript that can be used to create private variables and create functions that have persistent memories.
Example:
function outerFunction(x) {
let y = x;
return function innerFunction(z) {
return y + z;
}
}
let myClosure = outerFunction(5);
console.log(myClosure(10)); // 15
What is the purpose of the “use strict” directive?
The “use strict” directive is used to enable strict mode, which is a way of writing JavaScript code that helps to prevent errors and improve safety. It enforces stricter rules for code, which can help to prevent certain types of errors.
For example, consider the following code:
function myFunction() {
x = 10;
}
myFunction();
console.log(x); // prints 10
Without strict mode, this code would execute without any errors. However, when using strict mode, the code will throw an error because the variable x was not declared before it was used.
“use strict”;
function myFunction() {
x = 10; // throws an error
}
myFunction();
What is the difference between == and ===?
== is the equality operator and is used to compare two values. It doesn’t check the data type of the two values being compared. For example:
let a = 10;
let b = “10”;
a == b // returns true
=== is the strict equality operator and is used to compare two values. It checks the data type of the two values being compared. For example:
let a = 10;
let b = “10”;
a === b // returns false