JavaScript Logical Output Based Interview Questions
You mostly seen in JavaScript interviews there interviewers must asks output based questions in which candidate stuck mostly so here in this blog I'm telling you most commonly asked output based JavaScript interview questions.
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| By Education Funda |
Most Commonly Asked JavaScript Output Based Questions
Question: 1
function sum(){
let a = 8;const b=2;
var c=a+b;
}
console.log(a)
sum()
console.log(a)
// Reference error: a is not defined
console.log(b)
// Reference error: a is not defined
// Reference error: a is not defined
console.log(c)
// Reference error: a is not defined
console.log(a)
// Reference error: a is not defined
console.log(b)
// Reference error: b is not defined
console.log(c)
//Output: undefined
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Question: 2
let arr=[1,2,3,4,5];
console.log(arr[2], arr.length);
//Output: 3 5
arr.length=0;
console.log(arr[2], arr.length);
//Output: undefined 0
Note: As we can see in above code 1st questions is so easy but second is bit tricky one for second we are re-assigning the value of arr.length which logically we can do that's why after assign new value to arr.length our output is undefined for index value and 0 for arr.length.
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Question: 3
for (var i = 0; i < 3; i++) {
setTimeout(function() { alert(i); }, 1000 + i);
}
//Output: 3 3 3
Note: As we are using var so which is a global scope that's why as we are calling setTimeout which itself take time to RUN is call stack so within that time all Loops is finished that's why it takes last value which is 3 in each iteration.
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Question: 4
for(let i = 0; i <5; i++){
setTimeout(()=>{
console.log(i);
},0)
}
//Output: 0 1 2 3 4
Note: It relates to previous questions, as we are using let so which is a block scope that's why it keeps increase until loop didn't finished.
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Question: 5
let count = 0;
(function immediate() {
if (count === 0) {
let count = 1;
console.log(count); // What is logged?
}
console.log(count); // What is logged?
})();
//Output 1 0
Note: As we know code runs top to bottom so when go inside function count === 0 is TRUE as count variable defined before function called so output will be firstly 1 then 0 for second console.log().
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Question: 6
console.log(1+false); // Output: 1
console.log(1+true); // Output: 2
console.log(1-false); // Output: 1
console.log(1+'2'-1); // Output: 11
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Question: 7
(function fnA(a) { return (function fnB(b) { console.log(a); // What is logged? })(1); })(0);
//Output: 0
Note: It is immediate runs function as we are calling into () and as we can see we are calling function inside function which is also a Closure concept that's why we are able to get the value of variable b.
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