Javascript Interview 👨💻️ Questions Data Types
1. What are the falsy values in Javascript? Following are the falsy values
- ''
- 0
- null
- undefined
- false
- NaN 2. How to check if value is falsy? Use the ! ! operator or Boolean function to check if they’re falsy .
If a value is falsy , then both will return false .
! ! 0 // false 3. What are Wrapper Objects? Wrapper objects are objects that are created from constructors that return primitive values but have the type 'object' if it’s a number or a string . Symbols and BigInt have their own types .
Primitive values are temporarily converted to wrapper objects to call methods .
'foo' . toUpperCase ( )
Then we get `FOO` . It works by converting the 'foo' literal to an object and then call the toUpperCase ( ) method on it . 4. What is the difference between Implicit and Explicit Coercian Implicit coercion means that the JavaScript interpreter converts a piece of data from one type to another without explicitly calling a method .
1 + '2' // 12
Explicit conversion is done by calling a method or using an operator to convert a type .
+ '1' + + '2' // 3
gets us 3 since we have '1' and '2' are both converted to numbers by the unary + operator . 5. What Does 0 || 1 Return? Since 0 is falsy , it’ll trigger the second operand to run , which gives us 1. Therefore , it should return 1. 6. What Does 0 && 1 Return? Since 0 is falsy , it’ll stop running since we have short - circuited evaluation . Therefore , we get 0 returned . 7. What Does false == ‘0’ Return? false is falsy and '0' is converted to 0 , which is falsy , so they are the same in terms of the == ’s comparison criteria . Therefore , we should get true returned . 8. What Does 4 < 5 < 6 Return? In JavaScript , comparisons are done from left to right . So first 4 < 5 will be evaluated , which gives us true . Then true < 6 is evaluated , which is converted to 1 < 6 which is also true .
Therefore , we get true returned . 9. What Does typeof undefined == typeof null Return? typeof undefined returns 'undefined' and typeof null returns 'object' .
Since 'undefined' does equal 'object' , the expression should be false . 10. What Does typeof typeof 10 Return? JavaScript evaluates typeof typeof 10 as typeof ( typeof 10 ) . Therefore , this returns typeof 'number' , which returns 'string' since 'number' is a string .