Useful for when you have to move from one JIRA workflow to another but don't want to repeat the mapping for every fucking issue type.

jira-issue-map-copy.js

/**
 * Duplicate the mapping of Current Status to New Status from the first
 * issue type to the subsequent issue types.
 */

var tbody = document.getElementById('workflow-mapping-table').querySelector('tbody');
var cell = tbody.appendChild(document.createElement('tr')).appendChild(document.createElement('td'));
cell.setAttribute("colspan", 3);
cell.style.textAlign = "right";

var button = cell.appendChild(document.createElement('a'));
button.className = 'aui-button';
button.appendChild(document.createTextNode("Duplicate mapping ↓"));

button.onclick = function() {
    Array.prototype.slice.call(tbody.querySelectorAll('select[name^=mapping]'))
        .map(function(select) { return select.name.split('_').pop(); })
        .forEach(function(id) {
            var query='select[name^=mapping][name$=_'+id+']',
                first = document.querySelector(query);
            Array.prototype.splice.call(document.querySelectorAll(query), 1)
                .forEach(function(select) {
                    select.selectedIndex = first.selectedIndex;
                });
        });
};