javascript函数运行乱序

Question

In a Chrome Extension, I am trying to get saved information from the option page and use it in a content script. I am passing a message to the background script to get it. I have surrounded the sendMessage in the content script in a temporary function(I think that's what it's called) so that I could store the color outside of it. Unfortunatly it leads to things running about out of order. The output from the code below is:

3red

1red

2blue

I assume this has something to deal with the fact that I have created a temporary function.

Content_script.js:

    (function(){
        chrome.runtime.sendMessage({method: "getLocalStorage", key: "favColor"},
             function(response) {
                 console.log("1"+color);
                 color = response.data;
                 console.log("2"+color);
             }
        )
     })(color);

console.log("3"+color);
a.style.backgroundColor = color;

Background.js:

chrome.runtime.onMessage.addListener(function(request, sender, sendResponse) {
    if (request.method == "getLocalStorage")
      sendResponse({data: localStorage[request.key]});
    else
      sendResponse({}); // snub them.
});

Answer 1

The problem here is that the chrome runtime is running asynchronously. So when you execute that first function, it won't log those 1 and 2 messages until after the response is sent. It registers the callback and proceeds with the rest of the script. Since it takes a little bit of time for the runtime to respond, even though it may be fast, it won't receive a message back until after it's already logged 3 to the console.