Develop Reference

Is there any way to read what was printed to console programatically in JS? (For testing)

I have some automated tests written in TruClient scripts and I want to verify what was printed in the application JS console.
Is there any way to access that from the javascript?
Like console.getText() type of thing?
I want to verify that some information appeared in the console.
For instance, how can I do this?
console.log("Hi");
//Now I want to check if it was printed correctly in the browser
if(console.getText() == "Hi")
{
//then test passed
}
I am needing this because we are architecting new browsers.

You might be able to intercept calls to console by redefining them:
// Save original console methods
var originalConsole = {
log: console.log,
warn: console.warn,
error: console.error
}
var consoleHistory = [];
console.log = function() {
// Save inputs given to console.log()
consoleHistory.push(arguments);
// Make call to original console
originalConsole.log.apply(window.console, arguments);
}
// Repeat for warn and error, if needed.
Eloquent JavaScript uses this technique to display errors when evaluating JS in its code sandbox.

Script not printing error in JavaScript Chrome console

I have just spent far too long trying to find a problem with the code below.
In turned out that because of the context that addRoute was called in, keys() was not returning the keys of the results object. To fix this I had to use Object.keys() despite it working without a problem in the JavaScript console (which I later realised was because of the context).
My question is, why didn't this show in my JavaScript console? It took me quite a while to realise (I have cropped the full code, the actual function is a lot bigger).
Wrong, but no error in the console:
Map.prototype.addRoute = function (results) {
var sectionsIDs = keys(results);
}
Correct
Map.prototype.addRoute = function (results) {
var sectionsIDs = Object.keys(results);
}

Your first function uses the keys console API function.
That "Command Line API Reference" page includes the warning:
Note: This API is only available from within the console itself. You cannot access the Command Line API from scripts on the page.
Thus, it is by design that the keys function only exists for code run directly on the console.
Chrome gives you a small hint about the keys function being a console-only function if you view it in the console:
> keys
function keys(object) { [Command Line API] }

Cannot read property of undefined after Promise.promisify

let nasPath = "";
return getFamInfo(args.familyID)
.then(function (famInfo) {
nasPath = //some code involving famInfo here
return getSFTPConnection(config.nasSettings);
}).then(function (sftp) {
const fastPutProm = Promise.promisify(sftp.fastPut);
return fastPutProm(config.jpgDirectory, nasPath, {});
});
If I put a breakpoint after const fastPutProm = Promise.promisify(sftp.fastPut);, fastPutProm is a function with three arguments. But when I try to run this code, I get a TypeError: Cannot read property 'fastPut' of undefined error. What am I doing wrong here?

That error means that your sftp value is undefined so when you try to pass sftp.fastPut to the promisify() method, it generates an error because you're trying to reference undefined.fastPut which is a TypeError.
So, the solution is to back up a few steps and figure out why sftp doesn't have the desired value in it.
Another possibility is that the error is coming from inside the module and it's because the implementation of sftp.fastPut is referencing this which it expects to be sftp. Your method of promisifying is not preserving the value of this. You can fix that by changing your code to:
const fastPutProm = Promise.promisify(sftp.fastPut, {context: sftp});

Checking if specific console error occurred/exists with javascript

I would like to check if a certain console error has occurred using javascript, and alert() myself if it has.
The error will look like this:
00:00:34:0359 TimeEvent.COMPLETE
(anonymous function) # VM17617:1
And the algorithm will look something like this:
function checkError(console) {
if(console.error === "TimeEvent.COMPLETE") {
alert("The error is present");
}
}
I'm not very familiar with the console, and haven't gotten much further with Google research. Can somebody point me in the right direction?

I ultimately solved my question by following this blog post on taking over the console with javascript.
Here is my final code:
var original = window.console
window.console = {
error: function(){
//Gets text from error message.
errorText = arguments['0'];
if (errorText.includes('TimeEvent.COMPLETE')) {
//DO STUFF HERE
}
original.error.apply(original, arguments)
}
}

You didn't provide the whole picture about how and when the console is getting the error. If you raise the error yourself, or if you are able to catch it inside a try catch, that would be the best place to intercept those errors.
However, if you have no control about how those error are raised, you should try to intercept your console's error calls. I never tried it myself but this SO answer explains how to intercept the console's log calls. Knowing that the console usually have a function named error that is similar to the log function, I'm sure you could apply the same logic to intercept the errors sent to the console.
If you are using chrome, you may refer to the console documentation for more details about the error function. I'm not sure if there's a standard butInternet Explorer and Firefox also has support for console error function.

Uncaught TypeError: Cannot read property 'value' of null, need some direction

I have been trying to figure out this particular problem in my developer tools, but I've had no luck thus far. I have an error on one of my js files that says
Uncaught TypeError: Cannot read property 'value' of null
The following error refers to the 1st variable of dt_version below. The particular thing is if I comment out the first line of code. I get the same error on the following variables of offload1 and offload2. The variable is a number that I am trying to get passed over. I run this function on my body when the page loads...onload=updatetotal();
function updatetotal() {
var dt_version = document.getElementById("dt_version").value-0;
var offload1 = document.getElementById("capacity_offload1").value-0;
var offload2 = document.getElementById("capacity_offload2").value-0;
var offload3 = document.getElementById("capacity_offload3").value-0;
}
If a run an if statement looking for document.getElementByID("dt_version");...it defaults to false..so its not being carried over though on the previous page, I can see its input fine with the value in it. What am I missing here guys?

This error means that the id dt_version does not exist. Check your html to make sure it is there:
var dt = document.getElementById("dt_version");
if (dt){
// do your stuff
}else {
console.log("dt does not exist")
}

Another cause for this error may be- as you are calling the javascript function on page load there is a possible chance that your control is not yet completely rendered to the page. A simple solution is just move that control to the beginning of the page. If it doesn't work then an reliable solution is, call the function inside jquery $(document).ready().