Today #Day123 of #365DaysOfCode, Learning Essential JavaScript Interview Questions.

13. What will the code below output to the console and why?

console.log(1 +  "2" + "2");
console.log(1 +  +"2" + "2");
console.log(1 +  -"1" + "2");
console.log(+"1" +  "1" + "2");
console.log( "A" - "B" + "2");
console.log( "A" - "B" + 2);

Output:

"122"
"32"
"02"
"112"
"NaN2"
NaN

14. The following recursive code will cause a stack overflow if the array list is too large. How can you fix this and still retain the recursive pattern?

var list = readHugeList();

var nextListItem = function() {
    var item = list.pop();

    if (item) {
        // process the list item...
        nextListItem();
    }
};

The potential stack overflow can be avoided by modifying the nextListItem function as follows:

var list = readHugeList();

var nextListItem = function() {
    var item = list.pop();

    if (item) {
        // process the list item...
        setTimeout( nextListItem, 0);
    }
};

The stack overflow is eliminated because the event loop handles the recursion, not the call stack.

When nextListItem runs, if item is not null, the timeout function (nextListItem) is pushed to the event queue and the function exits, thereby leaving the call stack clear.

When the event queue runs its timed-out event, the next item is processed and a timer is set to again invoke nextListItem.

Accordingly, the method is processed from start to finish without a direct recursive call, so the call stack remains clear, regardless of the number of iterations.

Closures in JavaScript

function counter(){
    let count = 0
    return function() {
        count++
        console.log(count);
    }
}
const mycounter = counter()
mycounter()
mycounter()
mycounter()
mycounter()
mycounter()

{
    function counter(){
        let count = 0
        return function() {
            count++
            console.log(count);
        }
    }
    const mycounter = counter()()
    console.log(mycounter);
    const mycounter2 = counter()()
    counter()()
}

Conclusion

Learned and practiced Essential JavaScript Interview Questions involving topics like strings and number data types and setTimeout & closures in JavaScript.

Code

1. code

   

Source: JavaScript Interview Questions [Link]

Author: Dheeraj.y

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