for loop execution technicality

Question

I have a quick question about 'for' loops. Here is the code taken from one of the lessons:

for (var counter = 10;counter; counter = counter - 1) {
    console.log("Hello World", counter);
}

Is it just understood that the 'counter' variable declaration will only get run once in a for loop? In an initial examination, I would have expected counter to get set to 10 on each loop execution.

Therefore 'counter' would never get to be less than 9, and it would be an infinite loop. Can anyone explain why the 'var counter = 10' gets skipped over on subsequent executions of the loop?

Answer 1 · 2014-12-22T17:55:14Z

December 22, 2014 5:55pm

The formatting of the statements in the parentheses of a for loop are as follows

for(/*Initial variable assignment that only runs once*/; /*Condition that will determine if the loop runs each time*/; /*Event that should occur when each iteration is run that could change the condition*/){
    //Looping code here
}

Thus, the for loop you described looks something like this (with minor code readability improvements): <pre>

/*                 Condition that checks
                    if counter is not falsey
                       (i.e. not 0)
                     (checked every time)
   Initial assignment      |     Decrements the counter variable
        (runs once)        |       (runs every time)
                   |       |          |                    */
for (var counter = 10; counter; counter--) {
    console.log("Hello World", counter);
}

</pre>

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Vincent Asta

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for loop execution technicality

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Michael Hulet

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Vincent Asta

Vincent Asta

Michael Hulet

Michael Hulet