import k3d
import numpy as np

N = 1000
line = k3d.line(np.cumsum(np.random.randn(N,3).astype(np.float32),axis=0), 
                shader='mesh',
                width = 0.2,
                custom_data = {"test": 123})

plot = k3d.plot(custom_data={"test": 321})
plot += line
plot.display()

code = [
    "console.log(K3DInstance.getWorld().ObjectsListJson[%s].custom_data);" % (line.id),
    "console.log(K3DInstance.parameters.customData);"
]
with open("./custom_data.html", "w") as f:
    f.write(
        plot.get_snapshot(
            additional_js_code="\n".join(code)
        )
    )