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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) ?


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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