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Rapid fire 28 javascript questions and answers .

 

Rapid fire 28 javascript questions and answers .


Check these rapid javascript questions and answers that will help you to understand Javascript in a different way.

Question 1: What is typeof [] ?


Ans: Object. Actually, Array is derived from Object. If you want to check the array use Array.isArray(arr)


Question 2: What is typeof arguments?


Ans: Object. arguments are array-like but not array. it has length, can access by index but can't push pop, etc.


Question 3: What is 2+true?


Ans: 3. The plus operator between a number and a boolean or two boolean will convert boolean to number. Hence, true converts to 1 and you get a result of 2+1


Question 4: What is '6'+9 ?


Ans: 69. If one of the operands of the plus (+) operator is a string it will convert other numbers or boolean to string and perform concatenation. For the same reason, "2"+true will return "2true"


Question 5: What is the value of 4+3+2+"1" ?


Ans: 91 . The addition starts from the left, 4+3 results 7 and 7+2 is 9. So far, the plus operator is performing addition as both the operands are number. After that 9 + "1" where one of the operands is string and plus operator will perform concatenation.


Question 6: What is the value of "1"+2+4 ?


Ans: "124". For this one "1" + 2 will produce "12" and "12"+4 will generates "124".


Question 7: What is the value of -'34'+10 ?


Ans: -24. minus(-) in front of a string is an unary operator that will convert the string to a number and will make it negative. Hence, -'34' becomes, -34 and then plus (+) will perform simple addition as both the operands are number.


Question 8: What is the value of +'dude' ?


Ans: NaN. The plus (+) operator in front of a string is an unary operator that will try to convert the string to number. Here, JavaScript will fail to convert the "dude" to a number and will produce NaN.


Question 9: If you have var y = 1, x = y = typeof x; What is the value of x?


Ans: "undefined"


Question 10: for var a = (2, 3, 5); what is the value of a?


Ans: 5. The comma operator evaluates each of its operands (from left to right) and returns the value of the last operand. ref: MDN


Question 11: for var a = (1, 5 - 1) * 2 what is the value of a?


Ans: 8


Question 12: What is the value of !'bang' ?


Ans: false. ! is NOT. If you put ! in front of truthy values, it will return false. Using !! (double bang) is a tricky way to check anything truthy or falsy by avoiding implicit type conversion of == comparison.


Question 13: What is the value of parseFloat('12.3.4')?


Ans: 12.3


Question 14: What is the value of Math.max([2,3,4,5]) ?


Ans: NaN


Question 15: 3 instanceof Number ? 

Ans: false


Question 16:null == undefined ?


Ans: true


Question 17:What is the value of !!function(){};


Ans: true


Question 18: What is the value of typeof bar ?


Ans: "undefined"


Question 19: What is the value of typeof null?


Ans: "object"


Question 20: If var a = 2, b =3 what would be value of a && b ?

Ans: 3


Question 21: What would be consoled var foo = 'outside'; function logIt(){console.log(foo); var foo = 'inside';} logIt() ?


Ans: undefined


Question 22: What is -5%2 ?


Ans:-1. the result of remainder always get the symbol of first operand.


Question 23: Why .1+.2 != .3 ?


Ans: Because the answer will be 0.30000000000000004.

For more details click  here. 


Question 24: 42..toString() ?

Ans: "42"


Question 25: 4.2..toString ?

Ans: SyntaxError: Unexpected token .


Question 26:42 . toString() ?


Ans: "42"


Question 27: typeof(NaN) ?


Ans:"number"


Question 28: 2 in [1,2]?

Ans: false. Because "in" returns whether a particular property/index available in the Object. In this case, object has index 0 and 1 but don't have 2. Hence you get false.


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