问electron怎么下载文件暂停？

item.pause();会报未定义

// to store downloadItems

var downloadItems = [];

ipcMain.on('dowloadFiles', function(evt, options) {

if(options.command === 'startDownload') {

wc.downloadURL(file.url);

return;

}

if(options.command === 'stopDownload') {

var item = getDownloadItem(options.url);

item.pause();

return;

}

if(options.command === 'resumeDownload') {

var item = getDownloadItem(options.url);

item.resume();

return;

}

});

mainWindow.webContents.session.on('will-download', function(event, item, webContents) {

// Set the save path, making Electron not to prompt a save dialog.

item.setSavePath('c:\\downloadTest\\test.txt');

// store the download item, so that we can call item.pause/resume in a

downloadItems.push(item);

item.on('updated', function(event, state) {

// console.log('when updated send download progress to render process')

mainWindow.webContents.send('updateDownload', {

url: item.getURL(),

progress: item.getReceivedBytes() / item.getTotalBytes()

});

});

});