Question

From what I understand a option elements that popuate select elements in HTML are an array.
So basically what i want to do is return an array string that is separated by commas.

Tried to do selecbox.options.join(',');, but got an error that its not supported; anyone have an idea why?

Answer 1

It is not an array. It is an HTMLCollection. It is "array-like"

In 2022, a week before EOL of Internet Explorer 11, the simplest vanilla JavaScript solution is using spread and Array map

UPDATE: Array.from is actually preferable to the spread since it is more obvious what is going on

const opts = document.querySelectorAll("select option"); 
// we can use forEach on the resulting HTMLCollection 
// but map needs to be spread to array
const vals = Array.from(opts) // or [...opts]
  .map(el => el.value); 
console.log(vals);

<select>
<option value="Please select">Text 0</option>
<option value="one">Text 1</option>
<option value="two">Text 2</option>
<option value="three">Text 3</option>
</select><br/> 
The above select has the following option values:<br/>
<span id="result"></span>

---

Older answer that is compatible with IE11

from http://api.jquery.com/jQuery.each/ which CAN iterate over either:

Iterate over both objects and arrays.
Arrays and array-like objects with a
length property (such as a function’s
arguments object) are iterated by
numeric index, from 0 to length-1.
Other objects are iterated via their
named properties.

Each HTML Option element has a value and a text and some more attributes.

A simple for loop can be used

vals = []
var sel = document.querySelector("select");
for (var i=0, n=sel.options.length;i<n;i++) { // looping over the options
  if (sel.options[i].value) vals.push(sel.options[i].value);
}

the Array.apply posted by typeracer will return an array of HTMLOptionElements which still needs to be looped over or mapped to get at the values and texts

Here are a few versions that will return the same.

This fiddle will run in IE11 too

var vals, sel = document.querySelector("select"), show=function(vals) {$("#result").append("[" + vals.join("][") + "]<hr/>");}
var supportsES6 = function() {try{new Function("(a = 0) => a");return true;}catch (err) {return false;  }}();


// jQuery mapping jQuery objects - note the "this" and the .get()
vals = $('select > option').map(function() {return this.value;}).get();
show(vals);

// plain JS using loop over select options
vals = [];
for (var i = 0, n = sel.options.length; i < n; i++) { // looping over the options
  if (sel.options[i].value) vals.push(sel.options[i].value); // a bit of testing never hurts
}
show(vals);

// Plain JS using map of HTMLOptionElements - note the el
vals = Array.apply(null, sel.options).map(function(el) { return el.value; });
show(vals);

// ES6 JS using spread and map of HTMLOptionElements - note the fat arrow and el
if (supportsES6) 
  document.write(`<script>

  vals = [...sel.options].map(el => el.value);

show(vals);
<\/script>`
);

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<select>
<option value="Please select">Text 0</option>
<option value="one">Text 1</option>
<option value="two">Text 2</option>
<option value="three">Text 3</option>
</select><br/> 
The above select has the following option values:<br/>
<span id="result"></span>