JavaScript port of Ruby library Scientist, carefully refactoring critical paths

scientist.js

A JavaScript interpretation of the Ruby libraryScientist, a library for carefully refactoring critical paths.

How do I science?

Let's pretend you're changing the way you handle permissions in a large web app. Tests can help guide your refactoring, but you really want to capture the current and refactored beahviours under load.

ES6 Sample

import {Experiment, Result} from 'scientist.js';

import Permission from './permission';
import Model from './model';
class MyWidget {
    constructor() {
        this.model = new Model();
    }

allows(user) {
    var experiment = new Experiment("widget-permissions");
    experiment.use(() => this.model.checkUser(user).valid); // old way
    experiment.try(() => user.can(Permission.Read, this.model)); // new way

    return experiment.run();
}

}</pre> 
 
 Use use(..) to wrap the existing original behaviour, and use try(..) to wrap the new behaviour. experiment.run(); will always return the result of the use block, but it does a bunch of stuff behind the scenes: 

 
  
 It decides whether or not to run the try block 

  
 Randomises order to execute try and use blocks 

  
Measures the duration of both behaviours

  
 Swallows (but records) any exceptions raised in the try block and 

  
 Set a condition to filter calls to try 

 
 Upcoming features (these already exist in the Ruby library): 
 
  
 Compares the result of try to the result of use , 

  
Publishes all this information.

 
 The use block is called the control . The try block is called the candidate . 
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