v8-map-processor

v8-map-processor

Processes and visualizes maps (aka hidden classes) created by v8 during execution.

Derived from the one included with v8/tools.

Installation

npm install -g v8-map-processor

Usage

Create the Log File and Load it into the Browser

• Install a compatible Node.js or V8 runtime
  • a) Install Node.js >=v10 from nodejs.org or elsewhere
  • b) Install d8 via npm install -g jsvu
    • note that d8 is named v8 so either link it to d8 or use v8 when typing the next command
• Run your app with the --trace-maps flag, i.e. <node|d8> --trace-maps example/points.js
  • note that if running with d8 functionality like setTimeout, console.log and process are not available
• Run v8-map-processor in the same directory to load the produced v8.log into the maps visualizer

Interpreting the Result

The Stats view will show constructor and function names which can be selected to show more information regarding related maps.

To focus on the maps created as part of the example, once you load the visualizer scroll to the very right of the timeline to skip the maps that are created during initialization. Then you can click on any of the bars do get more info.

In the case you ran with Node.js you'll see an overwhelming amount of data and may have to find the maps you are interested in by searching for the constructor name via Cmd|Ctrl-f (in the example case Point) and then selecting it in the Stats view.

The following keyboard shortcuts are available:

• arrow up: select previous edge
• arrow down: select next edge
• arrow left: move to previous chunk
• arrow right: move to next chunk
• +: increase timeline resolution
• -: decrease timeline resolution