js &&符号的用法 语法问题请教各位大神
window.startCapture = function(a, b) {
a && a.w && a.h &&
(remoteRes = a, log && log.info("Receiver resolution: " + a.w + " X " + a.h));
singalChannelCallback = b;
request && request.currentSel && 2 == request.currentSel ? d(sourcePage) : desktopMediaRequestId = chrome.desktopCapture.chooseDesktopMedia(["screen"], onAccessApproved)
};
window.startWebRTC = function(a) { a && a.source && (sourcePage = a.source);
startSignalChanel() }
};
就这段a && a.w && a.h && 是什么意思啊 该怎么解读