How to use preload.js properly in Electron

问题

I'm trying to use Node modules (in this example, fs) in my renderer processes, like this:

// main_window.js
const fs = require('fs')

function action() {
    console.log(fs)
}

^{Note: The action function gets called when I press a button in my main_window.}

But this gives an error:

Uncaught ReferenceError: require is not defined
    at main_window.js:1

I can solve this issue, as suggested by this accepted answer, by adding these lines to my main.js when initializing the main_window:

// main.js
main_window = new BrowserWindow({
    width: 650,
    height: 550,
    webPreferences: {
        nodeIntegration: true
    }
})

But, according to the docs, this isn't the best thing to do, and I should instead, create a preload.js file and load these Node modules there and then use it in all of my renderer processes. Like this:

main.js:

main_window = new BrowserWindow({
    width: 650,
    height: 550,
    webPreferences: {
        preload: path.join(app.getAppPath(), 'preload.js')
    }
})

preload.js:

const fs = require('fs')

window.test = function() {
    console.log(fs)
}

main_window.js:

function action() {
    window.test()
}

And it works!

Now my question is, isn't it counter-intuitive that I should write most of the code of my renderer processes in preload.js (Because only in preload.js I have access to Node modules) and then merely call the functions in each renderer.js file (for example here, main_window.js)? What am I not understanding here?

回答1:

To do it securely, you'll want to set everything up like this. This is outlined in my comment here.

main.js

const {
  app,
  BrowserWindow,
  ipcMain
} = require("electron");
const path = require("path");
const fs = require("fs");

// Keep a global reference of the window object, if you don't, the window will
// be closed automatically when the JavaScript object is garbage collected.
let win;

async function createWindow() {

  // Create the browser window.
  win = new BrowserWindow({
    width: 800,
    height: 600,
    webPreferences: {
      nodeIntegration: false, // is default value after Electron v5
      contextIsolation: true, // protect against prototype pollution
      enableRemoteModule: false, // turn off remote
      preload: path.join(__dirname, "preload.js") // use a preload script
    }
  });

  // Load app
  win.loadFile(path.join(__dirname, "dist/index.html"));

  // rest of code..
}

app.on("ready", createWindow);

ipcMain.on("toMain", (event, args) => {
  fs.readFile("path/to/file", (error, data) => {
    // Do something with file contents

    // Send result back to renderer process
    win.webContents.send("fromMain", responseObj);
  });
});

preload.js

const {
    contextBridge,
    ipcRenderer
} = require("electron");

// Expose protected methods that allow the renderer process to use
// the ipcRenderer without exposing the entire object
contextBridge.exposeInMainWorld(
    "api", {
        send: (channel, data) => {
            // whitelist channels
            let validChannels = ["toMain"];
            if (validChannels.includes(channel)) {
                ipcRenderer.send(channel, data);
            }
        },
        receive: (channel, func) => {
            let validChannels = ["fromMain"];
            if (validChannels.includes(channel)) {
                // Deliberately strip event as it includes `sender` 
                ipcRenderer.on(channel, (event, ...args) => fn(...args));
            }
        }
    }
);

index.html

<!doctype html>
<html lang="en-US">
<head>
    <meta charset="utf-8"/>
    <title>Title</title>
</head>
<body>
    <script>
        window.api.receive("fromMain", (data) => {
            console.log(`Received ${data} from main process`);
        });
        window.api.send("toMain", "some data");
    </script>
</body>
</html>

来源：https://stackoverflow.com/questions/57807459/how-to-use-preload-js-properly-in-electron

标签

javascript

node.js

electron