Automatically populate a matrix field by injecting jQuery into the fields instructions.

auto-populate-matrix

<script>
$(function() {

// Make sure that this is the publish form
if (!EE.publish)
    return;

// Only proceed when creating a new entry
var entryId = $('#publishForm').find('input[name="entry_id"]').val();
if (entryId != 0)
    return;

function initLabels(id, labels) {
    var addEntryButton = $('#sub_hold_field_' + id + ' .matrix-btn.matrix-add');
    if (!addEntryButton.length)
        return;

    // Need to wait after `document.ready` has finished executing!
    setTimeout(function() {
        var field = $('#sub_hold_field_' + id);

        // Only proceed if matrix is empty
        // Note: This is not the case if a validation error occurs!
        if (!field.find('.matrix-norows').is(':visible'))
            return;

        // Create one row for each label
        for (var i = 0; i < labels.length; ++i)
            addEntryButton.click();

        // Skip the placeholder row for "No rows have been added yet..."
        field.find('tbody tr:not(.matrix-norows)').each(function(i) {
            $(this).find('.matrix-firstcell textarea').val(labels[i]);
        });
    }, 0);
}

// Check that this is an entry of the expected channel field group
if (EE.publish.field_group == 8) {
    // "Custom Parameters"
    initLabels('132', [
        'Sydney',
        'Melbourne'
    ]);
}

})
</script>