karabiner://karabiner/assets/complex_modifications/import?url=file:/Users/mping/Devel/workspace/capslock_ijkl_fn.json

capslock_ijkl_fn.json

{
  "title": "Caps Lock (Fn) + IJKL",
  "rules": [
    { "description": "Caps Lock to fn",
      "manipulators": [{"type": "basic", "from": {"key_code": "caps_lock", "modifiers": {"optional": ["any"]}}, "to": [{"key_code": "fn"}]}] },
    { "description": "Fn + I/J/K/L to Arrow Keys",
      "manipulators": [{"type": "basic", "from": {"key_code": "i", "modifiers": {"mandatory": ["fn"], "optional": ["any"]}}, "to": [{"key_code": "up_arrow"}] },
                       {"type": "basic", "from": {"key_code": "j", "modifiers": {"mandatory": ["fn"], "optional": ["any"]}}, "to": [{"key_code": "left_arrow"}]},
                       {"type": "basic", "from": {"key_code": "k", "modifiers": {"mandatory": ["fn"], "optional": ["any"]}}, "to": [{"key_code": "down_arrow"}]},
                       {"type": "basic", "from": {"key_code": "l", "modifiers": {"mandatory": ["fn"], "optional": ["any"]}}, "to": [{"key_code": "right_arrow"}]}] },
    { "description": "Fn + H to Delete",
      "manipulators": [{"type": "basic", "from": {"key_code": "h", "modifiers": {"mandatory": ["fn"], "optional": ["any"]}}, "to": [{"key_code": "delete_or_backspace"}]}] },
    { "description": "Disable arrows",
      "manipulators": [{"type": "basic", "from": {"key_code": "left_arrow"},  "to": [{"key_code": "vk_none"}]},
                       {"type": "basic", "from": {"key_code": "right_arrow"}, "to": [{"key_code": "vk_none"}]},
                       {"type": "basic", "from": {"key_code": "up_arrow"},    "to": [{"key_code": "vk_none"}]},
                       {"type": "basic", "from": {"key_code": "down_arrow"},  "to": [{"key_code": "vk_none"}]}] },
    { "description": "Disable Delete",
      "manipulators": [{"type": "basic", "from": {"key_code": "delete_or_backspace"},  "to": [{"key_code": "vk_none"}]}] }
  ]
}

Open karabiner://karabiner/assets/complex_modifications/import?url=file:/Users/mping/Devel/workspace/capslock_ijkl_fn.json in brower url

On Karabiner/Complex Modifications/Parameters, make sure to set to_if_held_down_threshold_milliseconds to a value high enough otherwise, long press on Caps Lock will eventually revert to normal behaviour