封闭混乱，在功能之间共享全局变量

Question

    var data = null;

    socket.on('screen1', function (data) {

        data = data;
        console.log(data) // has something
    });

    $approve.click(function(){
        console.log(data) //null
        socket.emit('screen2', data);

    });

For some reason I can't put click event into socket.on because it's listening to the server. But I want its callback which is the data .I tried to do data = data and expect my click callback is able to get the data but it's still null.

Answer 1

Your local variable takes precedence over the global variable:

socket.on('screen1', function (data) { // <-- local variable "data"
    data = data;  // <-- both these "data" are the same variable!!
});

To access the global variable "data" rename the local variable to something else:

socket.on('screen1', function (d) {
    // Here I have no idea what your intention is. If I am
    // confused consider how the compiler is supposed to read
    // your mind.

    // You either wanted to do:
    d = data;

    // or data = d;

    // I cannot guess and neither can the compiler.
});