how to copy only checked checkboxes to clipboard

I want to add a "copy to clipboard" button that copies only the checked checkboxes. with line break between contents. This is what i have so far (copies everything and without line break). please help.

The Button:

    <a:commandButton
                    id="copyURLsToClipboard" value="Copy to Clipboard"
                    style="width: 120px;"
                    onclick="onCopyClipboardClicked('#{urlAction.escapeJavaScript()}'); simulateClick(this); return false;"
                    onfocus="highlightButton(this);"
                    onblur="unhighlightButton(this);" />

The JS function:

function onCopyClipboardClicked(text) {
    if (window.clipboardData && clipboardData.setData) {
        clipboardData.setData("Text", text);
    } else {
        alert("Clipboard not found");
    }
}

The checkboxes:

                <div id="urlsContainer" class="list-group"
                    style='width: 350px; word-wrap: break-word;margin-top: 10px'>
                    <a:repeat value="#{urlAction.urlsIndexList}" var="_urlIndex">
                        <a href='#' class='list-group-item'
                            style='float: left; width: 350px; height: 50px;'>
                            <input
                            type='checkbox' class="urlCheckBox" name='checkbox-1'
                            style='margin-left: 15px; float: left;'><span
                                style='margin-left: 10px; font-size: 12px; float: left; word-break: break-all; width: 300px;'
                                onclick='showFraim("#{_urlIndex}")'>#{urlAction.getUrl(_urlIndex)}</span>
                            </input>
                        </a>
                    </a:repeat>
                </div>

I have all the URLs in the list named "urls" in a java class named urlAction. this is the java function escapeJavaScript():

public List<String> escapeJavaScript() {
    if (urls == null ) return null;
    List <String> stringUrls = new ArrayList<>();
    for ( AggregateUrl au : urls) {             
        stringUrls.add(escapeJavaScript(au.getUrl()));
    }
    return stringUrls;
}

Example:

[x]  www.google.com
[ ]  www.yahoo.com
[x]  www.nytimes.com

If I checked the first and third what would be copied to clipboard is this:

www.google.com
www.nytimes.com