json_encode

json_encode(value, array?) converts a Lua table or value into a JSON string. Uses SpyWeb’s built-in high-performance JSON engine, handling nested tables, arrays, booleans, and nulls automatically.

Empty Lua tables {} serialize as {} by default. Use JSON_EMPTY_ARRAY to force [], or pass array=true to treat all empty tables as arrays.

Signature

json_encode(value, array?)

sync

Parameters

Param	Type	Description
value	any	The Lua value to encode
array?	boolean	If true, all genuinely empty tables become []. Defaults to false.

Returns

Value	Type	Description
json	string	JSON-encoded string

Examples

Basic usage

local payload = {
    url = "https://example.com",
    options = { waitUntil = "networkidle2" }
}
local body = json_encode(payload)
local resp = http_post("https://api.rendering-service.com/render", body, {["Content-Type"]="application/json"})

Empty arrays

-- Empty tables become {} by default
json_encode({})                    -- "{}"

-- Use JSON_EMPTY_ARRAY to force []
json_encode(JSON_EMPTY_ARRAY)      -- "[]"
json_encode({ items = JSON_EMPTY_ARRAY })  -- '{"items":[]}'

-- Or use array=true blanket override
json_encode({ items = {} }, true)  -- '{"items":[]}'

Server response

get.data = function(self)
    return {
        status = 200,
        body = json_encode({
            items = JSON_EMPTY_ARRAY,
            meta = {}  -- this stays as {}
        }),
    }
end

See Also

• JSON_EMPTY_ARRAY - Sentinel value for empty JSON arrays
• json_decode - Parse JSON string to Lua table