Openalgo Chart Terminal

Build or extend a terminal. This is the largest thing you can build with this library, so build it in the order below and get each layer working before starting the next.

Two working references exist. Read the one closer to the user's stack before writing code:

• examples/yfinance/index.html in the openalgo-charts repo - a native-ESM terminal shell with modules under src/, no framework.
• frontend/src/components/trading/ChartPane.tsx and frontend/src/lib/trading/terminal.ts in the OpenAlgo application repo - a production React terminal. Its central lesson: keep chart orchestration in a plain TypeScript module and let React own only the DOM shell.

For async startup, pagination, replay entry/exit and concurrent registration, read host-integration. The widget already implements its documented reconnect recovery; a custom terminal must protect every data writer, including polling and older-history responses.

For an Objects panel, use the base-tier ChartObjects inventory described in core-api. Own one model per live chart generation, route drawing actions through its existing controller, and destroy the model before replacing the chart. Register profile capabilities explicitly; order and position primitives are outside the inventory. Persist indicator visible with its settings, defaulting older layouts to true. A custom React panel should clear old rows immediately when its focused chart changes. Packaged hosts can use widget.openObjects() and the existing editors.

Build order

1. Chart and data

import { createChart, darkTheme, OpenAlgoLiveDataFeed } from 'openalgo-charts';

const chart = createChart(el, { theme: darkTheme, crosshairMode: 'magnet' });
const price = chart.addSeries('candlestick');
const volume = chart.addSeries('histogram', { paneIndex: 1 });

Load history, then subscribe, seeding the builder from the last historical bar so the live candle continues its bucket instead of starting a fresh one. See feeds-and-live.

Wrap the feed in withBarCache before anything else touches it. A terminal reloads the same series constantly (symbol flicking, interval pills, a page refresh), and the wrapper turns those into warm reads. It never stores the forming bar, so what comes back is short by at most the bar the live subscription is about to send you anyway.

const feed = withBarCache(new OpenAlgoLiveDataFeed(cfg), { ttlMs: 60_000 });

Two things a terminal has to do itself. Show the verdict: a status line saying "warm 1 ms" against "fetched 320 ms" is the only way anyone can tell the cache is working, and feed.stats() gives you the hits. And cap to at the newest bar that can exist when the venue is shut: a hit past the entry's coverage is only allowed while the next bar is still forming, and the cache cannot know a market is closed, so out of hours every load is cold without the cap. You already have a session table for the clock; reuse it.

2. Symbol and interval switching

Switching either one is a full data reload, not a chart rebuild. Tear down the old subscription first, then setData, then resubscribe. Do not create a second chart.

Every code on the interval pills must resolve. s/m/h/d/w are built in; anything else (monthly, quarterly, a 500-tick bar) is a registerInterval call carrying a Bucketing rule, and an unregistered code now throws UnknownIntervalError at subscribe time rather than quietly drawing minute bars. Validate with isKnownInterval when the code can come from the user, and bucket calendar codes with bucketStartOf, never with a seconds-per-month constant: a month is 28 to 31 days and a New York month is not a Mumbai month.

registerInterval({ code: '1MO', bucketing: { mode: 'calendar', unit: 'month', count: 1 } });

Switch the clock with the symbol. chart.setTimezone(zoneForExchange(exchange)) takes an IANA name (default Asia/Kolkata) and moves the axis labels, the crosshair tag and every session-anchored study, so a US symbol stops restarting its VWAP in the middle of the afternoon. Hold the chosen zone in your own state if anything in the terminal rebuilds the chart, and offer it as a control: a user watching a US symbol from Mumbai may want either clock. The settings schema ships that control (time.timezone, step 10), so mirror the zone rather than building a second picker. It throws on a name the runtime does not know, so guard user input with isValidTimezone. See data-and-time.

3. History paging

chart.setHistoryLoader(fn) fires when the user pans past the left edge. Fetch older bars, series.prependData(older), then chart.historyLoadComplete(). Prepending shifts logical indices but the visible window is preserved - do not re-fit.

For a recent-bar default, use navigation.defaultVisibleBars and resetScale() after a symbol load that should adopt it. This is independent of the REST lookback. An explicit saved viewport still applies after data. Keep paging behind a request-owner guard so an old response or finally cannot alter a replacement chart or a newer request.

4. Chart type and transforms

The picker maps a label to a SeriesType. Renko, Range, Line Break and Heikin Ashi transform the bars you pass to an ordinary series; Point and Figure and Kagi need import 'openalgo-charts/transform' for their renderers. See transforms.

5. Indicators

import 'openalgo-charts/indicators', then a menu built from registeredIndicators(). The gear on a pane legend emits indicatorSettings - open your own dialog generated from the descriptor. See indicators.

6. Drawing rail

import { DrawingController } from 'openalgo-charts/draw';
const draw = new DrawingController(chart, { magnet: true });
draw.setTool('trend-line');

The controller is headless. Build the rail from registeredDrawingTools() and show the chord from drawingShortcuts() beside each name. The library installs no key listener - call matchDrawingShortcut(event) from your own handler, gated on the chart having focus and no dialog being open. See drawing-tools.

Wire Ctrl+C / Ctrl+X / Ctrl+V to draw.copy(), draw.cut() and draw.paste() in the same handler, and show the chords in the drawing's right-click menu. All three are async: await the cut, because it deletes only after the clipboard write succeeds and its boolean is the difference between "gone" and "still there". A paste of foreign clipboard content resolves to an empty array rather than throwing, so treat that as nothing to paste, not as an error to report.

7. On-chart trading

Two distinct layers. Get this right or you will build the wrong one.

The loop is: push exchange state into chart.trading, the user drags a line, the chart emits a trading:* event, your handler calls the broker, the broker's response comes back as new exchange state which you push in again. The chart is never the source of truth. See trading and trade-tier.

Ship analyzer/sandbox mode first and default to it. Nothing should reach a live broker until the user explicitly arms it.

8. Market depth

DomLadder from the trade tier, fed by subscribeDepth on the feed. Levels range from 5 to 200 depending on what the broker streams.

9. Layout persistence

localStorage.setItem('layout', JSON.stringify(chart.getState()));
chart.restoreState(JSON.parse(localStorage.getItem('layout')!));

One payload covers viewport, grid, panes, price scales, indicator instances, drawings and the settings block (canvas, status line, trading colours, event filters). Indicators whose tier is not loaded are skipped on restore rather than throwing, so restore after your tier imports. See events-and-state.