Implicit Execution & Proxies

Using ctx.run()

Instead of manually writing for(let i = bounds.startIndex; i <= bounds.endIndex; i++), you can wrap your time-series logic inside a ctx.run() callback. The engine will loop over all bars for you.

ctx.run((bar, state) => {
  // Logic executes on every bar!
});

State Persistence (The 'var' keyword)

In Pine Script, you use the var keyword to initialize a variable once and persist it across bars. In BacktestX, you use the state object.

ctx.run((bar, state) => {
  // Initialize only if undefined
  state.crossCount = state.crossCount ?? 0;
  
  if (ctx.ta.crossover(bar.close, ctx.ta.sma(ctx.bars.map(b => b.close), 14))[bar.index]) {
    state.crossCount++;
  }
});

JavaScript Proxies (close[1])

The bar object passed into the callback contains properties for open, high, low, close, and volume. These are not standard numbers; they are ES6 Proxy Objects.

This allows you to access historical data relative to the current bar by passing a lookback integer into the brackets.

• bar.close[0]: The current bar's close price.
• bar.close[1]: The previous bar's close price.
• bar.close[10]: The close price 10 bars ago.