My Karabiner rules containing "WASD arrow Keys toggled by Capslock". See https://stackoverflow.com/a/53698322/412916

karabiner.json

{
    "global": {
        "check_for_updates_on_startup": true,
        "show_in_menu_bar": true,
        "show_profile_name_in_menu_bar": false
    },
    "profiles": [
        {
            "complex_modifications": {
                "parameters": {
                    "basic.simultaneous_threshold_milliseconds": 50,
                    "basic.to_delayed_action_delay_milliseconds": 500,
                    "basic.to_if_alone_timeout_milliseconds": 1000,
                    "basic.to_if_held_down_threshold_milliseconds": 500
                },
                "rules": [
                    {
                        "description": "WASD arrow Keys toggled by Capslock",
                        "manipulators": [
                            {
                                "conditions": [
                                    {
                                        "name": "wasd_arrow_keys_mode",
                                        "type": "variable_unless",
                                        "value": 1
                                    }
                                ],
                                "from": {
                                    "key_code": "caps_lock",
                                    "modifiers": {
                                        "optional": [
                                            "any"
                                        ]
                                    }
                                },
                                "to": [
                                    {
										"key_code": "caps_lock",
                                        "set_variable": {
                                            "name": "wasd_arrow_keys_mode",
                                            "value": 1
                                        }
                                    }
                                ],
                                "type": "basic"
                            },
                            {
                                "conditions": [
                                    {
                                        "name": "wasd_arrow_keys_mode",
                                        "type": "variable_if",
                                        "value": 1
                                    }
                                ],
                                "from": {
                                    "key_code": "caps_lock",
                                    "modifiers": {
                                        "optional": [
                                            "any"
                                        ]
                                    }
                                },
                                "to": [
                                    {
                                        "set_variable": {
                                            "name": "wasd_arrow_keys_mode",
                                            "value":  0
                                        }
                                    }
                                ],
                                "type": "basic"
                            },
                            {
                                "conditions": [
                                    {
                                        "name": "wasd_arrow_keys_mode",
                                        "type": "variable_if",
                                        "value": 1
                                    }
                                ],
                                "from": {
                                    "key_code": "a",
                                    "modifiers": {
                                        "optional": [
                                            "any"
                                        ]
                                    }
                                },
                                "to": [
                                    {
                                        "key_code": "left_arrow"
                                    }
                                ],
                                "type": "basic"
                            },
                            {
                                "conditions": [
                                    {
                                        "name": "wasd_arrow_keys_mode",
                                        "type": "variable_if",
                                        "value": 1
                                    }
                                ],
                                "from": {
                                    "key_code": "s",
                                    "modifiers": {
                                        "optional": [
                                            "any"
                                        ]
                                    }
                                },
                                "to": [
                                    {
                                        "key_code": "down_arrow"
                                    }
                                ],
                                "type": "basic"
                            },
                            {
                                "conditions": [
                                    {
                                        "name": "wasd_arrow_keys_mode",
                                        "type": "variable_if",
                                        "value": 1
                                    }
                                ],
                                "from": {
                                    "key_code": "w",
                                    "modifiers": {
                                        "optional": [
                                            "any"
                                        ]
                                    }
                                },
                                "to": [
                                    {
                                        "key_code": "up_arrow"
                                    }
                                ],
                                "type": "basic"
                            },
                            {
                                "conditions": [
                                    {
                                        "name": "wasd_arrow_keys_mode",
                                        "type": "variable_if",
                                        "value": 1
                                    }
                                ],
                                "from": {
                                    "key_code": "d",
                                    "modifiers": {
                                        "optional": [
                                            "any"
                                        ]
                                    }
                                },
                                "to": [
                                    {
                                        "key_code": "right_arrow"
                                    }
                                ],
                                "type": "basic"
                            }
                        ]
                    }
                ]
            },
            "devices": [
                {
                    "disable_built_in_keyboard_if_exists": false,
                    "fn_function_keys": [],
                    "identifiers": {
                        "is_keyboard": true,
                        "is_pointing_device": false,
                        "product_id": 636,
                        "vendor_id": 1452
                    },
                    "ignore": false,
                    "manipulate_caps_lock_led": true,
                    "simple_modifications": []
                }
            ],
            "fn_function_keys": [
                {
                    "from": {
                        "key_code": "f1"
                    },
                    "to": {
                        "consumer_key_code": "display_brightness_decrement"
                    }
                },
                {
                    "from": {
                        "key_code": "f2"
                    },
                    "to": {
                        "consumer_key_code": "display_brightness_increment"
                    }
                },
                {
                    "from": {
                        "key_code": "f3"
                    },
                    "to": {
                        "key_code": "mission_control"
                    }
                },
                {
                    "from": {
                        "key_code": "f4"
                    },
                    "to": {
                        "key_code": "launchpad"
                    }
                },
                {
                    "from": {
                        "key_code": "f5"
                    },
                    "to": {
                        "key_code": "illumination_decrement"
                    }
                },
                {
                    "from": {
                        "key_code": "f6"
                    },
                    "to": {
                        "key_code": "illumination_increment"
                    }
                },
                {
                    "from": {
                        "key_code": "f7"
                    },
                    "to": {
                        "consumer_key_code": "rewind"
                    }
                },
                {
                    "from": {
                        "key_code": "f8"
                    },
                    "to": {
                        "consumer_key_code": "play_or_pause"
                    }
                },
                {
                    "from": {
                        "key_code": "f9"
                    },
                    "to": {
                        "consumer_key_code": "fastforward"
                    }
                },
                {
                    "from": {
                        "key_code": "f10"
                    },
                    "to": {
                        "consumer_key_code": "mute"
                    }
                },
                {
                    "from": {
                        "key_code": "f11"
                    },
                    "to": {
                        "consumer_key_code": "volume_decrement"
                    }
                },
                {
                    "from": {
                        "key_code": "f12"
                    },
                    "to": {
                        "consumer_key_code": "volume_increment"
                    }
                }
            ],
            "name": "Default profile",
            "selected": true,
            "simple_modifications": [],
            "virtual_hid_keyboard": {
                "country_code": 0
            }
        }
    ]
}