Javascript 关闭和 WebRTC 回调问题

Question

我运行遇到了这个问题，我正在创建闭包并使用调试器单步执行，变量 connectingClientId 在闭包回调 (localOfferCreated) 中正确设置。当 createOffer 调用回调时，connectedClientId 未定义。怎么会这样呢？为了这个我整晚都在用头撞墙。

function publishStream(handShakeInitiator, connectingClientId) {
    var localOfferCreated = offerClosure(connectingClientId);
    var localIceCandidate = iceClosure(connectingClientId);
    peerConnections[connectingClientId] = new RTCPeerConnection(peerConnectionConfig);
    peerConnections[connectingClientId].onicecandidate = localIceCandidate;

    peerConnections[connectingClientId].addStream(localStream);

    if (handShakeInitiator) {
        peerConnections[connectingClientId].createOffer(localOfferCreated, createOfferError, offerOptions);
    }
}

function offerClosure(id) {

    var connectingClientId = id;

    function offerCreated(description) {
        peerConnections[connectingClientId].setLocalDescription(description, function (connectingClientId) {
            webSocket.send(JSON.stringify({
                'control': signalConstants.sendToClient,
                'cid': connectingClientId,
                'sdp': description
            }));
        }, function () {
            console.log('Error setting description.');
        });
    };

    return offerCreated;
}

从调试器中注意这些：

connectingClientId 已设置 -

调用时未设置 connectingClientId -

我在这里错过了什么？

Answer 1

来自RTCPeerConnection.setLocalDescription

successCallback
Is a Function without parameter which will be called when the description has been successfully set. At this point, one can send the offer to a remote server that can forward it to a remote client

您正在通过将其作为内部函数参数来重新定义 connectingClientID。请记住，命名函数参数是一个隐式变量声明，正如文档所说，它将是未定义的，因为成功回调不提供任何参数。 JavaScript 函数可以访问它们的外部范围，所以你的匿名函数不需要传递这个 arg，它可以简单地引用它创建一个闭包。

function offerCreated(description) {
    peerConnections[connectingClientId].setLocalDescription(description, function() {  
        webSocket.send(JSON.stringify({
            control: signalConstants.sendToClient,
            cid: connectingClientId,
            sdp: description
        }));
    }, function () {
        console.log('Error setting description.');
    });
};

Javascript 关闭和 WebRTC 回调问题

Javascript Closure and WebRTC callback issues

javascript

closures

callback

webrtc