proper use of the array.push method

Question

if I have a simple test function that adds even numbers to an array:

function isEven(n){
    var enumbers = [];
    if (n % 2 == 0){
        enumbers.push (n);
    }
}

how can I increment my parameter until I have a set number of members in my array? for instance, I've tried this:

function isEven(n){
    var enumbers = [];
    while ( enumbers.length < 10){
    if (n % 2 == 0){
        enumbers.push (n);
    }
    console.log (enumbers);
             n = n + 1;
    isEven(n);
    }
}
isEven(1);

but it seems to just create a new array for each number until it finally throws a range error (maximum call stack size exceeded).

your calling isEven recursivly inside your loop. So for every function call you actually call your function 10 additional times. — basilikum
– basilikum, Commented Jun 20, 2013 at 19:58
that was a typo... i had already corrected that but I got the same result. — kjarsenal
– kjarsenal, Commented Jun 20, 2013 at 19:59
keep evaluating numbers 1 through however many it takes to push a predetermined (in this case, 10) number of even numbers into the "enumbers" array. — kjarsenal
– kjarsenal, Commented Jun 20, 2013 at 20:06

tymeJV · Accepted Answer · 2013-06-20 19:58:35Z

2

It's creating that array multiple times because you're constantly calling that function with:

isEven(n);

You're also not comparing to the length of the array, just the array. Add .length to enumbers. Try changing to:

var enumbers = [];
while ( enumbers.length < 10){
    if (n % 2 == 0){
        enumbers.push (n);
    }
    console.log (enumbers);
}

answered Jun 20, 2013 at 19:58

tymeJV

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4 Comments

kjarsenal Over a year ago

The strategy was to keep calling isEven until the array had ten members. That's why I put it in a while loop. I think I just need to know how to properly increment the function parameter isEven(?)

tymeJV Over a year ago

You don't need to keep calling that, because each time you do, it re-initializes the array. Your while loop is taking care of the atleast 10 numbers part.

Bergi Over a year ago

@kjarsenal: Consider either calling a function that puts one number in the array repeatedly (recursively), or putting that functions' body in a loop. Not both.

kjarsenal Over a year ago

Thank you Bergi and Vitim. I think I misunderstood the way the while loop operates. Thanks for your help.

Victor · Accepted Answer · 2013-06-20 20:48:30Z

0

I'm not sure if I understood your question. But you shouldn't use global variables, and it is unnecessary to call your function recursively inside a while loop.

The error maximum call stack size exceeded is your browser trying to break a infinity loop.

This is what you need.

Examples here jsFiddle1 and jsFiddle2

function isEven(n) {
    var enumbers = [];

    while (enumbers.length < 10) {
        if (n % 2 == 0) {
            enumbers.push(n);
        }
        n++;
    }
    return enumbers;
}

Setup a test

var n = 1;
var evenArray = isEven(n); //call isEven function and it returns an array

document.body.innerHTML = evenArray; //2,4,6,8,10,12,14,16,18,20

edited Jun 20, 2013 at 20:48

answered Jun 20, 2013 at 20:15

Victor

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Comments

GolezTrol · Accepted Answer · 2013-06-20 19:57:10Z

0

The problem is that (enumber < 10) apparently always evaluates to true, causing an endless loop. But it is this comparison that is wrong, since you're comparing an integer with an array I think you're trying to get the array length?:

while (enumbers.length < 10) {

Another thing. enumbers is a local variable, so each call to isEven has it's own array. Therefore, the functions is called recursively, over and over again.

answered Jun 20, 2013 at 19:57

GolezTrol

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1 Comment

Bergi Over a year ago

That is now fixed. However, try [0,2,4] < 10…

dev2d · Accepted Answer · 2013-06-20 20:00:27Z

0

I suggest you create the array outside of is even method

answered Jun 20, 2013 at 20:00

dev2d

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Comments

Victor · Accepted Answer · 2013-06-20 20:04:46Z

-1

I would have written something like:

function isEven(n,enumbers){  
    while(enumbers < 10){  
        if (n % 2 == 0){  
             enumbers.push (n);  
        }
        console.log (enumbers);  
        n = n + 1;  
        isEven(n, enumbers);  
    }  
}  
var enumbers = [];  
isEven(1,enumbers);

edited Jun 20, 2013 at 20:04

Victor

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answered Jun 20, 2013 at 20:00

face

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2 Comments

kjarsenal Over a year ago

this actually is exactly what I was trying to accomplish. You just copied my codebase before I remembered to add .length to enumbers. this is great

Bergi Over a year ago

Please either use recursion or a while-loop

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