阅读console.log（）输出形式的javascript

Question

I am writing an overlay UI for one application using Greasemonkey, injecting JS to a page.

Now I have issue to hook on some ajax calls that runs on the webpage. However, the page is generating console logs, informing that content is fully loaded. My question is:

In plain javascript, is there a possibility of reading console output generated by completely different script?

function blackBox(){
   //this is generating come console output.
   //this runs on code layer I have no access to.
}

function readConsole(){
   //read console record by record
   if(console.msg == "something I want"){
      doSomething();
   }

}

Thanks in advance :)

Answer 1

As others have stated, you can override the console.log() function with your own, and implement your own implementation:

var oldLog = unsafeWindow.console.log;
var messages = [];

unsafeWindow.console.log = function(msg) {
    messages.push(msg);
    oldLog.apply(null, arguments);
}

// Access the entire console.log history in messages

Answer 2

Redefine console.log and storage messages on a array:

var consoleStorage = [];

console.log = function(msg){
   consoleStorage.push(msg);
   console.warn(msg); // if you need to print the output
}

Now you can read all logs:

function readConsole(){
   //read console record by record
   consoleStorage.forEach(msg => {
      doSomething(msg);
   });
}

Answer 3

Even if it were possible, that would be bad practice. The console is for human eyes to see, when debugging. It usually takes several milliseconds to execute console.log , so executing it in production code is not a good idea.

I would say programming in booleans (like ifDidX and ifDidY ) would be better. But if you really had to do this message-history thing, a better alternative would be to store messages in some other array. Here is an example:

 var messagesLog = []; //Since console.log takes several milliseconds to execute, you should tick this to false in production code. const logToConsole = true; function logMessage( message ){ //adds message to JS log. messagesLog.push(message); //performs console.log if not production code if(logToConsole){ console.log(message); } } logMessage("pizza"); logMessage("second to last message"); logMessage("last message"); //checks last message and this will be true if( messagesLog[messagesLog.length - 1] == "last message" ){ logMessage("The last message in the log was 'last message'"); } //checks last message and this will be false if( messagesLog[messagesLog.length - 1] == "pizza" ){ logMessage("This will not occur because the last message was 'last message'"); } //searches through log to find certain message for(let i = 0; i < messagesLog.length; i++){ if(messagesLog[i] == "pizza"){ logMessage("one of the messages in the log was pizza"); } } 

Answer 4

Directly there's no way to access console outputs, but what you can do is that you can override console.log in a way where it checks for you condition first and then outputs the content, below is a sample code for that

console.stdlog = console.log.bind(console);
console.log = function(msg){
    if(msg == "something I want"){
    ...
    }
    console.stdlog.apply(console, arguments);
}

Although you'll need to be very careful with this since if you add any console.log in that condition, it will create an infinite loop.