Engineer @ Replay here - If you're a console.log kind of developer (isn't everyone at least some of the time?), you should check this out. Imagine being able to add console.log() statements to code that already ran and seeing the results immediately! It's a bit mind blowing the first time you use it.
The video next to "Print statements from the future" on the webpage shows a bit of it.
You can click on the line-number next to a line of code to add a print at that location. If you hover over the line-number, it'll show you a count (exact and correct) of how many times that line of code hit during execution. Clicking on it adds a print log at that line with a default string.
At that point, the console log in the left should change immediately to include a bunch of new entries with "Loading.." text that resolves to the text of each print statement.
Clicking on the string allows you to replace it with an expression to be evaluated. The expression can include references to local scope variables, etc.
If you edit the expression, the console entries for the prints go back to "Loading.." and the new values are resolved.
The prints in the console are ordered in time sequence along with all the other events that can be shown there (regular console logs, mouse and keyboard and other events, etc.)
