Top 10 JavaScript Interview Questions
1. What are the Truthy and Falsy values?
Answer: A truthy value is like true and a falsy value is like false. These are as follows:
falsy values -> 0, “”, undefined, null, NaN, false
truthy values-> “0” , “ “, [], {}, ‘false’So, If we use one of these values in the if-else statement then we will get the same output which is shown below. In this given example, I will show you these values using ternary expression inside the console.log() method.
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2. What is the difference between null and undefined?
Answer: Firstly, null means an empty or non-existent value. It is supposed to be something that doesn’t exist. It can be assigned to a variable as a representation of an empty value.
On the other hand, undefined means a variable has been declared but its value has not been assigned. In the function, If we don’t pass the parameters, it shows undefined.
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3. What is the difference between double equal (==) and triple equal (===)?
Answer: Double equal ==is an abstract equality operator. It checks whether its two operands are the same or not by changing the expression from one data type to another.
On the other hand, Triple equal === is a strict equality operator which returns false for the values which are not of a similar type. Triple Equals does not perform type coercion.
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4. What is 'this’ keyword?
Answer: It refers to an object which is executing the current bit of JavaScript code. While executing every JavaScript function has a reference to its current executing context, it's called this.
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5. How to check for a prime number?
Answer: A prime number is a natural number that is only divisible by 1 and itself. For example 2, 3, 5, 7 are the prime number. On the other hand, 4 is not a prime number because it is divisible by 1, 2, and 4 itself.
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6. Find the largest element of an array?
Answer: We can find the largest element of an array using the for-loop method.
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7. How to use the JavaScript callback function?
Answer: In JavaScript, we can pass a function as an argument to a function. This function that is passed as an argument inside of another function is called a callback function.
In this given code, there are two functions and while calling the greet() function, two arguments (a string value and a function) are passed.
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8. What is the difference between the Let and Const?
Answer: In the Es6 version of JavaScript, variables can be declared in two more ways. The first is that we can declare a variable with the keyword let.
By applying the keyword let we can change the value of the variable more than once. If we use the keyword let in a block scope then we will not access it outside of this block scope. We can also declare a variable by applying the keyword const. But its specialty is that the value of the variable cannot be changed more than once.
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9. What are the advantages of the Arrow function?
Answer: The arrow function is a method of shortcut to the function declaration. It will basically shorten our function syntax.
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10. Closure in JavaScript:
Answer: When a function is able to remember and access its lexical scope even when that function executing outside its lexical scope.
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