JavaScript Questions & Answers – JavaScript Extensions

This set of Javascript Multiple Choice Questions & Answers (MCQs) focuses on “JavaScript Extensions”.

1. What will be the output of the following JavaScript code?

const pi=3.14;
var pi=4;
console.log(pi);

a) This will flash an error
b) Prints 4
c) Prints 3.14
d) Ambiguity
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2. The let keyword cannot be used ___________
a) as a substitute of var
b) as a block statement to define new variables
c) to define variables that are scoped to a single expression
d) in a else if loop, as a substitute for var
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3. The main difference between the variables declared with var and with let is __________
a) var is confined to a particular function but let is not
b) let is confined to a particular function but var is not
c) var defines values based on conditions but let does not
d) let doesn’t let you change the value of the variable
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4. What will be the output of the following JavaScript code if oddsums(5); is executed after the following code snippet?

function oddsums(n) 
{
     let total = 0, result=[]; 
     for(let x = 1; x <= n; x++) 
     { 
        let odd = 2*x-1; 
        total += odd;
        result.push(total);
     }
     return result;
}

a) Returns [1,4,9,16,25]
b) Returns [1,2,3,4,5]
c) Returns [3,6,9,12,15]
d) Returns [1,3,5,7,9]
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5. What would be the result or type of error if p is not defined in the following JavaScript code snippet?

console.log(p)

a) Zero
b) Null
c) Reference Error
d) Value not found Error
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6. What will be the output of the following JavaScript code?

let x=x+1;
console.log(x);

a) 0
b) Null
c) Reference error
d) NaN
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7. What will be the output of the following JavaScript code?

[x,y]=[y,x];

a) Throws exception
b) Swap the value of the two variables
c) Flashes an error
d) Creates a new reference object
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8. Which looping statement allows XML tags to appear in JavaScript programs and adds API for operating on XML data?
a) for loop
b) while loop
c) for/each loop
d) do while loop
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9. Which exception does the Iterators throw from their next() method when there are no more values to iterate, that work on finite collections?
a) Exit Iteration
b) Abort Iteration
c) Abort
d) Stop Iteration
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10. Which method of the iterable object returns an iterator object for the collection?
a) iterator()
b) _iterator_()
c) _iteration_()
d) _return_iterator_()
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11. What will be the output of the following JavaScript code?

<p id="demo"></p>
<script>
function myFunction() 
{
   var res = "";
   res=res + Number.isSafeInteger(Math.pow(2, 53)-1)+": 2<sup>53</sup>-1<br>";
   document.getElementById("demo").innerHTML = res;
}
</script>

a) True
b) False
c) Error
d) Undefined
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12. What will be the output of the following JavaScript code?

<p id="demo"></p>
<script>
function myFunction() 
{
   document.getElementById("demo").innerHTML = Number.MAX_VALUE;
}
</script>

a) 1.7976931348623157e+308
b) 1.7976931348623157e+305
c) 1.7976931348623157e+307
d) Error
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13. What will be the output of the following JavaScript code?

<p id="demo"></p>
<script>
function myFunction() 
{
   document.getElementById("demo").innerHTML = Number.NEGATIVE_INFINITY;
}
</script>

a) -1000
b) -infinity
c) infinity
d) undefined
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14. What will be the output of the following JavaScript code?

<p id="demo"></p>
<script>
function myFunction() 
{
   var x = 100;
   document.getElementById("demo").innerHTML = x.NEGATIVE_INFINITY;
}
</script>

a) True
b) False
c) Error
d) Undefiend
View Answer

15. What will be the output of the following JavaScript code?

<p id="demo"></p>
<script>
function myFunction() 
{
   var num = 5.56789;
   var n = num.toExponential();
   document.getElementById("demo").innerHTML = n;
}
</script>

a) 5.56789e+0
b) 5.57e+0
c) 5.568e+0
d) Error
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Sanfoundry Global Education & Learning Series – Javascript Programming.

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