LanternUI

Native Phoenix LiveView UI components — server-rendered SVG charts (and more over time), themeable via CSS variables. No React, no JavaScript charting library.

Part of the lantern family: lantern is an embeddable Postgres table viewer; lantern_ui is the UI component set.

What's here

• LanternUI.Charts.area_chart/1 — time-series area + line with an interactive crosshair/tooltip.
• LanternUI.Charts.sparkline/1 — compact trend, no axes.
• LanternUI.Charts.bar_chart/1 — categorical bars.
• LanternUI.Charts.line_chart/1 — multi-series time-series lines with a legend and a shared crosshair tooltip (built for resource/monitoring metrics).
• LanternUI.Charts.Geometry — pure scaling / "nice" ticks / SVG path helpers.

Geometry is computed in Elixir, so charts re-render through normal LiveView assigns. The only client JS is one small hook (ChartHover) for the area chart's tooltip.

Installation

From Hex (once published):

def deps do
  [{:lantern_ui, "~> 0.1"}]
end

Or from git while iterating:

{:lantern_ui, "~> 0.3"}
# or track main:
# {:lantern_ui, github: "go9/lantern-ui"}

Usage

<LanternUI.Charts.area_chart
  id="price-history"
  series={[%{date: "2024-01-01", value: 24.5}, %{date: "2024-02-01", value: 27.1}]}
  value_format={:currency}
  height={250}
/>

<LanternUI.Charts.sparkline id="trend" series={[3, 5, 4, 6, 8, 7, 9]} />

<LanternUI.Charts.bar_chart
  id="sales"
  series={[%{label: "Q1", value: 42}, %{label: "Q2", value: 31}]}
/>

<LanternUI.Charts.line_chart
  id="pod-cpu"
  series={[
    %{label: "web-1", color: "var(--color-primary)",
      points: [{~U[2024-11-20 14:00:00Z], 0.25}, {~U[2024-11-20 14:05:00Z], 0.31}]},
    %{label: "web-2", points: [{~U[2024-11-20 14:00:00Z], 0.18}, {~U[2024-11-20 14:05:00Z], 0.22}]}
  ]}
  value_format={&"#{&1} cores"}
/>

line_chart series: a list of %{label, color, points: [{datetime, number}]} (color optional; points accept {datetime, value} tuples or %{time, value} maps; datetime = DateTime/NaiveDateTime/Date/ISO-8601 string).

area_chart series: a list of %{date: iso8601 | Date, value: number}.

JS hook (required for area_chart hover)

area_chart uses ChartHover and line_chart uses LineHover for their crosshair/tooltips — both ship in LanternHooks, so the single import below registers them. In assets/js/app.js:

import LanternHooks from "../../deps/lantern_ui/priv/static/lantern_ui_hooks.js"

let Hooks = { ...LanternHooks /* , ...yourOtherHooks */ }
let liveSocket = new LiveSocket("/live", Socket, { params: {/* ... */}, hooks: Hooks })

sparkline and bar_chart need no JavaScript.

Theming

Components read colors from CSS variables with chained fallbacks:

• Using Fluxon (or any system defining those tokens)? Do nothing — charts inherit your tokens through the fallbacks and match automatically. Don't import the bundled theme (it would override with its own --lantern-*).

• Standalone / public? Import the optional light + dark theme:

  /* assets/css/app.css */
  @import "../../deps/lantern_ui/priv/static/lantern_ui.css";

• Recolor by setting any --lantern-* variable yourself.

Value formatting

area_chart and bar_chart accept value_format: :number (default), :currency (USD-style $ prefix), or a 1-arity function (number -> String.t()). Any other value is treated as :number. Custom-function output is rendered as plain text — it is HTML-escaped before it reaches the tooltip.

License

MIT — see LICENSE.