Chrome extension: sendMessage doesn't work

Question

I\'ve already read the documentation from Google on \'message passing\' a few times and have probably looked at over 10 other questions with the same problem and already tri

Answer 1

Here is the solution, using background script:

manifest.json

{
    "manifest_version" : 2,
    "name" : "Message Test",
    "version" : "1.0",

    "background":{
        "scripts":["popup.js"]
    },

    "content_scripts": [
        {
        "matches" : [""],
        "js": ["message-test.js"]
        }
    ]
}

message-test.js

var port = chrome.runtime.connect();
port.onMessage.addListener(function(message, sender, sendResponse) {
    if (message.greeting == "Can you hear me?"){
        alert("Test");
    }
    else{
        sendResponse({});
    }
});

popup.js

chrome.runtime.onConnect.addListener( function ( port ) {
port.postMessage({
        greeting: "Can you hear me?"
    });
});

Some explanaition: first we are connecting to our background script from content script and then background script sends message to content script.

Update

I've improved answer according to @Xan remark. But the idea is the same, first of all you should let know your background script of the existence of content script.