//Add data
for (var col = 1; col < 6; col++) {
    for (var row = 2; row < 11; row++) {
        activeSheet.setValue(row, col, row + col);
    }
}

$("#button1").click(function () {
var columns = [ { firstCol: 3, lastCol: 5 } ];
spread.options.allowUndo = true;
spread.commandManager().execute({cmd: "resizeColumn", sheetName: "Sheet1", columns:columns, value: 50, isRowHeader: false});
    });

<input type="button" id="button1" value="button1"/>