Pace

A node.js module that outputs a progress bar and other metrics to the command-line. It was originally conceived to help measure the 'pace' of long running scripts.

We've used it to optimize scripts that would have taken hours to complete down to minutes, without having to wait the hours before knowing that the script could use some optimization.

Note: This module is not longer maintained but you are welcome to PR or fork. You might want to check:

• ascii-progress - Ascii progress-bar(s) in the terminal
• node-multimeter - render multiple progress bars at once on the terminal

Installation

$ npm install pace

Example

Running the following code:

var total = 50000,
    count = 0,
    pace = require('pace')(total);

while (count++ < total) {
  pace.op();

  // Cause some work to be done.
  for (var i = 0; i < 1000000; i++) {
    count = count;
  }
}

Usage

Pace object

The module exports a factory function to generate instances of Pace objects. So require('pace')(<options>) creates an instance of Pace, passing options to the constructor.

Options

Options can either be an object literal, or an integer. If its an integer then it is the same as passing options with only the total specified.

require('pace')(100);

// Same as

require('pace')({total: 100});

Supported Options:

• total - The total number of operations that YOUR script will execute.
• maxBurden - The maximum 'burden' that the progress bar should incur. See more about burden below.
• showBurden - Mostly for debugging. Show the current burden / skipped steps with the other metrics.
• hideFinishMessage - Hides the message displayed when the progress bar finishes. Default: False
• finishMessage - Pass a custom message to display when the progress bar finishes. Default: Finished!
• errorMessage - Pass a custom message to display when a signal error has been passed.

pace.op([count])

Signal to pace that an operation was completed in your script by calling pace.op().

If you would rather track the progress in your own logic, you can call pace.op(<count>) where <count> is the current operation interation (for example step # 50 of a 100 step process).

pace.op({errors: count})

Signal to pace that an error has happened. This will automatically signal a normal count increase but will also increase the error counter shown under the progress bar. Note: The errors count can be passed to be more than one, however each error signal triggers one op() count.

pace.total

If your script has a dynamic amount of work to do (for example, depending on the results of previous operation there may be more steps to complete), you can freely change the value of pace.total. Just set the value like: pace.total = 200.

Burden

Depending on how intensive your operations are, calculating, formatting, and printing the progress bar might be much more expensive than the work you are doing. It would be silly if printing a progress bar caused your job to take significantly longer than it would have otherwise. Pace tracks a stat called 'burden', which is basically a percentage of the overall execution time that is being spent inside the progress bar logic itself.

The default maxBurden is 0.5, which translates to 0.5% of the total execution time. If this low burden is causing you to see progress reported less often than you would prefer, you can raise it to something like 20 (20%) via the maxBurden option.

Examples

The test/ folder contains some simple test scripts you can run to see the progress bar in action.

Common Issues

Multiple writes and wrong progress bar rendering

If you have multiple instances of pace running in various parts of your application, from the second run onwards you might notice that the progress bar is not rendered correctly with duplicate output. This effect is additive for each time pace is required with the same stream.

Cause: The problem is with pace dependency charm. In node.js 0.10 the EventEmitter constructor explicitly initializes this._events, so going Charm.prototype = new Stream; causes all Charm instances to share the same _events property.

Fix: Change the charm main module file index.js and replace Charm.prototype = new Stream; with Charm.prototype = Stream.prototype;

References:

• substack/node-charm/#18