Memory in SciChart.js is stored in WebAssembly (Wasm) buffers via the type SCRTDoubleVector. It cannot be treated like a JavaScript array, however it is possible to bulk write/read to these arrays or to get/set at index.

You can access values on a DataSeries by getting the internal WebAssembly native arrays via getNativeXValues() and getNativeYValues(). These return SCRTDoubleVector - a webassembly buffer type which stores underlying data as Float64 array.

const xyDataSeries = new XyDataSeries(wasmContext);
xyDataSeries.appendRange([1,2,3], [10,20,30]);
const xValues = xyDataSeries.getNativeXValues();
const yValues = xyDataSeries.getNativeYValues();
for(let i = 0; i < xyDataSeries.count(); i++) {
    console.log(`index=${i}, xy = ${xValues.get(i)}, ${yValues.get(i)}`);
}

// Will output to console
// index=0, xy=1, 10
// index=1, xy=2, 20
// index=2, xy=3, 30

Examples of Dynamic Updates

There are a number of worked examples of how to apply dynamic updates to the chart over at the page DataSeries Realtime Updates.