The ExcelScript API is the set of objects and methods that Office Scripts use to manipulate a workbook: Workbook, Worksheet, Range, Table, and so on. Reads and writes are done with methods such as getRange, getValues and setValues, and writing a block of values at once is faster than cell by cell.
Example
const plage = sheet.getRange("A1:C10");
const valeurs = plage.getValues();