Why do nested for loops work in the way that they do in the following example:

var times = [
            ["04/11/10", "86kg"], 
            ["05/12/11", "90kg"],
            ["06/12/11", "89kg"]
];

for (var i = 0; i < times.length; i++) {
        var newTimes = [];
        for(var x = 0; x < times[i].length; x++) {
            newTimes.push(times[i][x]);
            console.log(newTimes);  


        }

    }

In this example I would have thought console.log would give me the following output:

["04/11/10"]
["86kg"]
["05/12/11"]
["90kg"]
["06/12/11"]
["89kg"]

However, I actually get this:

["04/11/10"]
["04/11/10", "86kg"]
["05/12/11"]
["05/12/11", "90kg"]
["06/12/11"]
["06/12/11", "89kg"]

Is anyone able to help me understand this?

EDIT:

Thanks for all your responses!

Why do nested for loops work in the way that they do in the following example:

var times = [
            ["04/11/10", "86kg"], 
            ["05/12/11", "90kg"],
            ["06/12/11", "89kg"]
];

for (var i = 0; i < times.length; i++) {
        var newTimes = [];
        for(var x = 0; x < times[i].length; x++) {
            newTimes.push(times[i][x]);
            console.log(newTimes);  


        }

    }

In this example I would have thought console.log would give me the following output:

["04/11/10"]
["86kg"]
["05/12/11"]
["90kg"]
["06/12/11"]
["89kg"]

However, I actually get this:

["04/11/10"]
["04/11/10", "86kg"]
["05/12/11"]
["05/12/11", "90kg"]
["06/12/11"]
["06/12/11", "89kg"]

Is anyone able to help me understand this?

EDIT:

Thanks for all your responses!

• javascript
• arrays
• for-loop

5 Answers 5

You are redefining newTimes on every single loop and you are outputting to the console on each column push.

var times = [
            ["04/11/10", "86kg"], 
            ["05/12/11", "90kg"],
            ["06/12/11", "89kg"]
];
 var newTimes = [];
for (var i = 0; i < times.length; i++) {     
        for(var x = 0; x < times[i].length; x++) {
            newTimes.push(times[i][x]);
        }
    }
    console.log(newTimes);  

Returns: ["04/11/10", "86kg", "05/12/11", "90kg", "06/12/11", "89kg"] http://jsfiddle.net/niklasvh/SuEdt/

// remember that the increment of the counter variable
// is always executed after each run of a loop


for (var i = 0; i < n; i++) {
    // some statement(s) to do something.. 

        // initializes child-loop counter in the first run of the parent-loop
        // resets child-loop counter in all following runs of the parent-loop
        // while i is greater than 0 and lower than n

    for (var j = 0; j < p; j++) {
        // some statement(s) to do something..

            // initializes grandchild-loop counter in the first run of the child-loop
            // resets grandchild-loop counter in all following runs of the child-loop
            // while j is greater than 0 and lower than p

        for (var k = 0; k < q; k++) {
            // some statement(s) to do something..
            // or add more internal loop-nestings if you like..
        }
    }
}

// if the counter variables of the descendent-loops were set before the loop-nesting,
// the inner loops would only run once, because the counter would keep the value
// of the abortion condition after the loop is finished

Do this:

var newTimes = [];
for (var i = 0; i < times.length; i++) {
        for(var x = 0; x < times[i].length; x++) {
            newTimes.push(times[i][x]);
            console.log(newTimes);  


        }

    }

You are re-initializing newTimes each time through the loop.

You output would be appropriate if the log statement would read

console.log(times[i][x]);

Instead you output your complete new list newTimes which is initialized outside the inner loop and grows with each inner loop iteration.

The problem is in the second round of the inner loop, where it pushes the second element into newTimes. Anyway I don't understand the reason of inner loop. You can write much simpler:

var times = [
            ["04/11/10", "86kg"], 
            ["05/12/11", "90kg"],
            ["06/12/11", "89kg"]
];

for (var i = 0; i < times.length; i++) {
    console.log(time[i][0]);  
    console.log(time[i][1]);   
}