In Javascript While loop repeats last number when counting from 1 to 5 when run on console [duplicate]

Question

When running following code on console:

var counter=0; while(counter<5){ console.log(counter); counter++; }

console o\p: 0 1 2 3 4 4

whereas for following code works fine, without repeating last value:

for(var i=0; i<5; i++){ console.log(i); }

console o\p: 0 1 2 3 4

Now, if I place above for loop after above mentioned while loop , output is perfectly fine:

var counter=0; while(counter<5){ console.log(counter); counter++; } for(var i=0; i<5; i++){ console.log(i); }

console o\p: 0 1 2 3 4 0 1 2 3 4

whereas, if I place while loop after for loop , repetition of last number found.

for(var i=0; i<5; i++){ console.log(i); } var counter=0;while(counter<5){ console.log(counter); counter++; }

console o\p: 0 1 2 3 4 0 1 2 3 4 4

Request all to provide a reason on this unexpected behavior of while loop. Thanks.

Answer 1

When performing operations in the console, the return value of the last executed line is always output.

That means that simply writing

var counter = 0; ++counter;

will log 1 to the console.

The same is happening in your loop, the return value of the last counter++ is output to the console as the value of the last executed expression.

Answer 2

The output of the log method depends on the javascript engine of the browser. The last value printed is not output of the loop itself.

Try: var counter=0; while(counter<5){ console.log(counter++); }