Hold caps (as esc) for vim arrows with Hammerspoon

EDIT March 6, 2025

This post was originally about using Hammerspoon to get my Caps Lock key (which is remapped to esc) + h,j,k, and l to function as vim arrow keys. However, it didn’t always work and caused some input lag.

I’ve since switched to Karabiner elements for this same functionality. Here’s the karabiner rule I’m using now:

{
    "description": "CAPS as ESC, CAPS held + H/J/K/L as ←↓↑→, CAPS held + D/U as PG↓↑",
    "manipulators": [
        {
            "conditions": [
                {
                    "name": "caps_lock pressed",
                    "type": "variable_if",
                    "value": 1
                }
            ],
            "from": {
                "key_code": "j",
                "modifiers": { "optional": ["any"] }
            },
            "to": [{ "key_code": "down_arrow" }],
            "type": "basic"
        },
        {
            "conditions": [
                {
                    "name": "caps_lock pressed",
                    "type": "variable_if",
                    "value": 1
                }
            ],
            "from": {
                "key_code": "k",
                "modifiers": { "optional": ["any"] }
            },
            "to": [{ "key_code": "up_arrow" }],
            "type": "basic"
        },
        {
            "conditions": [
                {
                    "name": "caps_lock pressed",
                    "type": "variable_if",
                    "value": 1
                }
            ],
            "from": {
                "key_code": "h",
                "modifiers": { "optional": ["any"] }
            },
            "to": [{ "key_code": "left_arrow" }],
            "type": "basic"
        },
        {
            "conditions": [
                {
                    "name": "caps_lock pressed",
                    "type": "variable_if",
                    "value": 1
                }
            ],
            "from": {
                "key_code": "l",
                "modifiers": { "optional": ["any"] }
            },
            "to": [{ "key_code": "right_arrow" }],
            "type": "basic"
        },
        {
            "conditions": [
                {
                    "name": "caps_lock pressed",
                    "type": "variable_if",
                    "value": 1
                }
            ],
            "from": {
                "key_code": "d",
                "modifiers": { "optional": ["any"] }
            },
            "to": [{ "key_code": "page_down" }],
            "type": "basic"
        },
        {
            "conditions": [
                {
                    "name": "caps_lock pressed",
                    "type": "variable_if",
                    "value": 1
                }
            ],
            "from": {
                "key_code": "u",
                "modifiers": { "optional": ["any"] }
            },
            "to": [{ "key_code": "page_up" }],
            "type": "basic"
        },
        {
            "from": {
                "key_code": "caps_lock",
                "modifiers": { "optional": ["any"] }
            },
            "to": [
                {
                    "set_variable": {
                        "name": "caps_lock pressed",
                        "value": 1
                    }
                }
            ],
            "to_after_key_up": [
                {
                    "set_variable": {
                        "name": "caps_lock pressed",
                        "value": 0
                    }
                }
            ],
            "to_if_alone": [{ "key_code": "escape" }],
            "type": "basic"
        }
    ]
}