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@jsvision/datagrid / windowedView

Function: windowedView() ​

windowedView<T>(source): T[]

Defined in: datagrid/src/windowing.ts:103

A length-correct, lazily-read view over a windowed source, presentable as the display: () => T[] the grid body demands. .length reports the source total; an integer index returns the loaded row or undefined (a hole is never collapsed away). It is typed T[], but only .length and integer indexing are supported — every whole-array operation (.map/.find/.reduce/spread/for..of) throws a descriptive error, because such an operation over a windowed source would either crash on the first unloaded row or full-scan the entire dataset (a fetch-storm). Route each whole-array consumer behind isWindowed and read source.rowAt(i) directly instead.

Type Parameters ​

T ​

T

Parameters ​

source ​

GridDataSource<T>

The windowed source to present as a lazy array.

Returns ​

T[]

A T[]-typed lazy view: length-correct, integer-indexable, and fail-loud on any other access.

Example ​

ts
import { windowedView } from '@jsvision/datagrid';
import type { GridDataSource } from '@jsvision/datagrid';
interface Row { id: number; name: string }
const loaded = new Map<number, Row>();
for (let i = 0; i < 50; i++) loaded.set(i, { id: i, name: `Row ${i}` });
const source: GridDataSource<Row> = {
  rowKey: (r) => r.id,
  length: () => 100000,
  rowAt: (i) => loaded.get(i),
  ensureRange: (start, end) => {
    // fetch rows [start, end) from the backing store and populate `loaded`
  },
};
const view = windowedView(source);   // source.length() === 100000, only rows [0,50) loaded
view.length;                         // 100000 (the source total)
view[10];                            // the loaded row
view[500];                           // undefined (an unloaded hole)
// view.map(...) or [...view] throws — gate the consumer behind isWindowed(source) first.