Google Spreadsheet JSON ExportHow-to at http://blog.pamelafox.org/2013/06/exporting-google-spreadsheet-as-json.html

exportjson.js

const EMPTY_VALUE = undefined;

// Includes functions for exporting active sheet or all sheets as JSON object (also Python object syntax compatible).
// Tweak the makePrettyJSON_ function to customize what kind of JSON to export.

function onOpen() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var menuEntries = [
    {name: "Export JSON for this sheet", functionName: "exportSheet"},
    {name: "Export JSON for all sheets", functionName: "exportAllSheets"}
  ];
  ss.addMenu("Export JSON", menuEntries);
}

function exportAllSheets() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheets = ss.getSheets();
  var sheetsData = {};
  for (var i = 0; i < sheets.length; i++) {
    var sheet = sheets[i];
    var rowsData = getRowsData_(sheet);
    var sheetName = sheet.getName(); 
    sheetsData[sheetName] = rowsData;
  }
  var json = makeJSON_(sheetsData);
  displayText_(json);
  return json;
}

function exportSheet() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  var rowsData = getRowsData_(sheet);
  var json = makeJSON_(rowsData);
  displayText_(json);
}

function makeJSON_(object) {
  var jsonString = JSON.stringify(object, null, 4);
  return jsonString;
}

function displayText_(text) {
  var output = HtmlService.createHtmlOutput("<textarea style='width:100%;' rows='20'>" + text + "</textarea>");
  output.setWidth(400)
  output.setHeight(300);
  SpreadsheetApp.getUi()
      .showModalDialog(output, 'Exported JSON');
}

/**
 * getRowsData iterates row by row in the input range and returns an array of objects.
 * Each object contains all the data for a given row, indexed by its normalized column name.
 * Arguments:
 *   - sheet: the sheet object that contains the data to be processed
 *   - range: the exact range of cells where the data is stored
 *   - columnHeadersRowIndex: specifies the row number where the column names are stored.
 *       This argument is optional and it defaults to the row immediately above range; 
 * Returns an Array of objects.
 */
function getRowsData_(sheet) {
  var headersRange = sheet.getRange(1, 1, sheet.getFrozenRows(), sheet.getMaxColumns());
  var headers = headersRange.getValues()[0];
  var dataRange = sheet.getRange(sheet.getFrozenRows()+1, 1, sheet.getLastRow(), headers.length);
  var objects = getObjects_(dataRange.getValues(), dataRange.getRichTextValues(), headers);
  return objects;
}

/**
 * getColumnsData iterates column by column in the input range and returns an array of objects.
 * Each object contains all the data for a given column, indexed by its normalized row name.
 * Arguments:
 *   - sheet: the sheet object that contains the data to be processed
 *   - range: the exact range of cells where the data is stored
 *   - rowHeadersColumnIndex: specifies the column number where the row names are stored.
 *       This argument is optional and it defaults to the column immediately left of the range; 
 * Returns an Array of objects.
 */
function getColumnsData_(sheet, range, rowHeadersColumnIndex) {
  rowHeadersColumnIndex = rowHeadersColumnIndex || range.getColumnIndex() - 1;
  var headersTmp = sheet.getRange(range.getRow(), rowHeadersColumnIndex, range.getLastRow(), 1).getValues();
  var headers = normalizeHeaders_(arrayTranspose_(headersTmp)[0]);
  return getObjects_(arrayTranspose_(range.getValues()), headers);
}

/**
 * For every row of data in data, generates an object that contains the data. Names of
 * object fields are defined in keys.
 * Arguments:
 *   - data: JavaScript 2d array
 *   - keys: Array of Strings that define the property names for the objects to create
 */
function getObjects_(data, richData, keys) {
  var isObject = false;
  var objects = [];
  if (keys[0] === "id") {
    objects = {};
    isObject = true;
  }
  for (var i = 0; i < data.length; ++i) {
    var id = false;
    var object = {};
    var hasData = keys.length;
    for (var j = 0; j < data[i].length; ++j) {
      var cellData = data[i][j];
      if (keys[j].includes("[richText]")) {
        cellData = htmlEncodeRichText_(richData[i][j]);
      } else {
        cellData = data[i][j];
      }
      if (isCellEmpty_(cellData)) {
        hasData--;
      }
      if (isObject && keys[j] === "id") {
        id = cellData;
      } else {
        setObjectData_(object, keys[j].replace("[richText]", ""), cellData);
      }
    }
    if (hasData !== 0) {
      if (isObject) {
        if (id !== undefined) {
          id = `${id}`;
          let arr = id.split(".");
          let obj = objects;
          for (let i in arr) {
            if (i == (arr.length - 1)) {
              if (Object.keys(object).length === 1 && object.value) {
                obj[arr[i]] = object.value;
              } else {
                  obj[arr[i]] = object;
              }
            } else if (!(arr[i] in obj)) {
              obj[arr[i]] = {};
            }
            obj = obj[arr[i]];
          }
        }
      } else{
          objects.push(object);
      }
    }
  }
  return objects;
}

/**
 * For every key in the keys array
 * recursively fill the object with data
 * Arguments:
 *   - object: JavaScript object to fill
 *   - keys: Array (or '.' separated String) that deifine the imbricated properties names for the object to fill
 *   - data: value that should be put
 */
function setObjectData_(object, keys, data) {
  if (!keys) return;
  if (!Array.isArray(keys)) {
    keys = keys.split(".");
  }
  if (keys.length == 1) {
    if (keys[0].charAt(0) === "@") {
      object.push({id: keys[0].substring(1), value: data});
    } else if (!(Array.isArray(object) && data == "")) {
      object[keys[0]] = data === "" ? EMPTY_VALUE : data;
    }
  } else {
    if (!object.hasOwnProperty(keys[0])) {
      if (!isNaN(keys[1]) || keys[1].charAt(0) === "@")
        object[keys[0]] = [];
      else
        object[keys[0]] = {};
    }
    setObjectData_(object[keys[0]], keys.slice(1), data);
  }
}

/**
 * Returns an Array of normalized Strings.
 * Arguments:
 *   - headers: Array of Strings to normalize
 */
function normalizeHeaders_(headers) {
  var keys = [];
  for (var i = 0; i < headers.length; ++i) {
    var key = normalizeHeader_(headers[i]);
    if (key.length > 0) {
      keys.push(key);
    }
  }
  return keys;
}

/**
 * Normalizes a string, by removing all alphanumeric characters and using mixed case
 * to separate words. The output will always start with a lower case letter.
 * This function is designed to produce JavaScript object property names.
 * Arguments:
 *   - header: string to normalize
 * Examples:
 *   "First Name" -> "firstName"
 *   "Market Cap (millions) -> "marketCapMillions
 *   "1 number at the beginning is ignored" -> "numberAtTheBeginningIsIgnored"
 * Keeps the "." for imbricated datas
 */
function normalizeHeader_(header) {
  var key = "";
  var upperCase = false;
  for (var i = 0; i < header.length; ++i) {
    var letter = header[i];
    if (letter == " " && key.length > 0) {
      upperCase = true;
      continue;
    }
    if (letter !== "_" && letter !== "@" && letter !== "." && !isAlnum_(letter)) {
      continue;
    }
    if (key.length == 0 && isDigit_(letter)) {
      continue; // first character must be a letter
    }
    if (upperCase) {
      upperCase = false;
      key += letter.toUpperCase();
    } else {
      key += letter.toLowerCase();
    }
  }
  return key;
}

/**
 * Returns true if the cell where cellData was read from is empty.
 * Arguments:
 *   - cellData: string
 */
function isCellEmpty_(cellData) {
  return typeof(cellData) == "string" && cellData == "";
}

/**
 *  Returns true if the character char is alphabetical, false otherwise.
 */
function isAlnum_(char) {
  return char >= 'A' && char <= 'Z' ||
    char >= 'a' && char <= 'z' ||
    isDigit_(char);
}

/**
 *  Returns true if the character char is a digit, false otherwise.
 */
function isDigit_(char) {
  return char >= '0' && char <= '9';
}

/**
 * Given a JavaScript 2d Array, this function returns the transposed table.
 * Arguments:
 *   - data: JavaScript 2d Array
 * Returns a JavaScript 2d Array
 * Example: arrayTranspose([[1,2,3],[4,5,6]]) returns [[1,4],[2,5],[3,6]].
 */
function arrayTranspose_(data) {
  if (data.length == 0 || data[0].length == 0) {
    return null;
  }

  var ret = [];
  for (var i = 0; i < data[0].length; ++i) {
    ret.push([]);
  }

  for (var i = 0; i < data.length; ++i) {
    for (var j = 0; j < data[i].length; ++j) {
      ret[j][i] = data[i][j];
    }
  }

  return ret;
}

/**
 * Given a RichTextValue Object, iterate over the individual runs
 *    and call out to htmlStyleRtRun() to return the text wrapped
 *    in <span> tags with specific styling.
 * @param {RichTextValue} richTextValue a RichTextValue object
 *    from a given Cell.
 * @return {string} HTML encoded text 
 */
function htmlEncodeRichText_(richTextValue) {
  return richTextValue.getRuns().reduce((s, r) => {
    text = r.getText().replace(/\n/g, "<br>");
    style = r.getTextStyle();
    if (style.isStrikethrough()) {
      text = "<strike>" + text + "</strike>";
    }
    if (style.isUnderline()) {
      text = "<u>" + text + "</u>";
    }
    if (style.isBold()) {
      text = "<b>" + text + "</b>";
    }
    if (style.isItalic()) {
      text = "<i>" + text + "</i>";
    }
    if (style.getFontSize() > 11) {
      text = "<big>" + text + "</big>";
    }
    if (style.getFontSize() < 11) {
      text = "<small>" + text + "</small>";
    }
    return s + text;
  }, "");
}

@florentdescroix Just wanted to say thanks for some nice code. Forced me to remember GoogleDoc stuff and I'm no expert so I guess your tutorial, comments and links are good enough!