window.js

// This helper remembers the size and position of your windows (and restores
// them in that place after app relaunch).
// Can be used for more than one window, just construct many
// instances of it and give each different name.

import { app, BrowserWindow, screen } from 'electron';
import jetpack from 'fs-jetpack';

export default function (name, options) {
  const userDataDir = jetpack.cwd(app.getPath('userData'));
  const stateStoreFile = 'window-state-' + name +'.json';
  var defaultSize = {
    width: options.width,
    height: options.height
  };
  let state = {};
  let win;

  var restore = function () {
    let restoredState = {};
    try {
      restoredState = userDataDir.read(stateStoreFile, 'json');
    } catch (err) {
      // For some reason json can't be read (might be corrupted).
      // No worries, we have defaults.
    }
    return Object.assign({}, defaultSize, restoredState);
  };

  const getCurrentPosition = function () {
    const [x, y] = win.getPosition();
    const [width, height] = win.getSize();

    return {
      x,
      y,
      width,
      height,
    };
  };

  const windowWithinBounds = function (windowState, bounds) {
    return windowState.x >= bounds.x &&
            windowState.y >= bounds.y &&
            windowState.x + windowState.width <= bounds.x + bounds.width &&
            windowState.y + windowState.height <= bounds.y + bounds.height;
  };

  var resetToDefaults = function () {
    const { bounds } = screen.getPrimaryDisplay();
    return Object.assign({}, defaultSize, {
      x: (bounds.width - defaultSize.width) / 2,
      y: (bounds.height - defaultSize.height) / 2
    });
  };

  const ensureVisibleOnSomeDisplay = function (windowState) {
    const visible = screen.getAllDisplays().some(function (display) {
      return windowWithinBounds(windowState, display.bounds);
    });
    if (!visible) {
      // Window is partially or fully not visible now.
      // Reset it to safe defaults.
      return resetToDefaults(windowState);
    }
    return windowState;
  };

  const saveState = function () {
    if (!win.isMinimized()) {
      Object.assign(state, getCurrentPosition());
    }
    userDataDir.write(stateStoreFile, state, { atomic: true });
  };

  state = ensureVisibleOnSomeDisplay(restore());

  win = new BrowserWindow(Object.assign({}, options, state));

  win.on('close', saveState);

  return win;
}