Karabiner Fn + HJKL / IJKL / WASD / ESDF as arrow keys

private.xml

<?xml version="1.0"?>
<root>
    <item>
        <name>F19 to Fn</name>
        <appendix>You can use Seil to map CapsLock to F19 (keycode 80)</appendix>
        <identifier>private.f19_to_fn</name>
        <autogen> __KeyToKey__ KeyCode::F19, KeyCode::FN </autogen>
    </item>
    <item>
        <name>Fn + HJKL as arrows</name>
        <appendix>Vim style</appendix>
        <identifier>private.fn_and_hjkl_as_arrows</name>
        <autogen> __KeyToKey__ KeyCode::K, ModifierFlag::FN, KeyCode::CURSOR_UP </autogen>
        <autogen> __KeyToKey__ KeyCode::H, ModifierFlag::FN, KeyCode::CURSOR_LEFT </autogen>
        <autogen> __KeyToKey__ KeyCode::J, ModifierFlag::FN, KeyCode::CURSOR_DOWN </autogen>
        <autogen> __KeyToKey__ KeyCode::L, ModifierFlag::FN, KeyCode::CURSOR_RIGHT </autogen>
    </item>
    <item>
        <name>Fn + IJKL as arrows</name>
        <identifier>private.fn_and_ijkl_as_arrows</name>
        <autogen> __KeyToKey__ KeyCode::I, ModifierFlag::FN, KeyCode::CURSOR_UP </autogen>
        <autogen> __KeyToKey__ KeyCode::J, ModifierFlag::FN, KeyCode::CURSOR_LEFT </autogen>
        <autogen> __KeyToKey__ KeyCode::K, ModifierFlag::FN, KeyCode::CURSOR_DOWN </autogen>
        <autogen> __KeyToKey__ KeyCode::L, ModifierFlag::FN, KeyCode::CURSOR_RIGHT </autogen>
    </item>
    <item>
        <name>Fn + WASD as arrows</name>
        <identifier>private.fn_and_wasd_as_arrows</name>
        <autogen> __KeyToKey__ KeyCode::W, ModifierFlag::FN, KeyCode::CURSOR_UP </autogen>
        <autogen> __KeyToKey__ KeyCode::A, ModifierFlag::FN, KeyCode::CURSOR_LEFT </autogen>
        <autogen> __KeyToKey__ KeyCode::S, ModifierFlag::FN, KeyCode::CURSOR_DOWN </autogen>
        <autogen> __KeyToKey__ KeyCode::D, ModifierFlag::FN, KeyCode::CURSOR_RIGHT </autogen>
    </item>
    <item>
        <name>Fn + ESDF as arrows</name>
        <identifier>private.fn_and_esdf_as_arrows</name>
        <autogen> __KeyToKey__ KeyCode::E, ModifierFlag::FN, KeyCode::CURSOR_UP </autogen>
        <autogen> __KeyToKey__ KeyCode::S, ModifierFlag::FN, KeyCode::CURSOR_LEFT </autogen>
        <autogen> __KeyToKey__ KeyCode::D, ModifierFlag::FN, KeyCode::CURSOR_DOWN </autogen>
        <autogen> __KeyToKey__ KeyCode::F, ModifierFlag::FN, KeyCode::CURSOR_RIGHT </autogen>
    </item>
</root>

How to using Fn+keys as arrow keys

Currently supporting Fn + IKJL, HJKL, WASD or ESDF

Install Karabiner

brew install Caskroom/cask/karabiner

Copy the contents of this private.xml into your custom Karabiner private.xml located at

~/Library/Application Support/Karabiner/private.xml

Open Karabiner. Click Reload XML and enable the style you want

Optionally you can map CapsLock as Fn:

brew install Caskroom/cask/seil

Open Seil. Map CapLock to Fn (keycode 63)