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).

• David Thomas: Test against enumbers.length?
• basilikum: your calling isEven recursivly inside your loop. So for every function call you actually call your function 10 additional times.
• kjarsenal: that was a typo... i had already corrected that but I got the same result.
• David Thomas: What is this function supposed to do?
• kjarsenal: 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.

Answer 1

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);
}

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

Answer 2

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

Answer 3

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.

• Bergi: That is now fixed. However, try [0,2,4] < 10...

Answer 4

I suggest you create the array outside of is even method

Answer 5

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);

• kjarsenal: 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: Please either use recursion or a while-loop