Strategy for evaluating + unit-testing Couchdb map, reduce, update functions

loader.js

const path = require("path")
const glob = require("glob")
const fs = require("fs")
const nodeEval = require("node-eval")

/** Helper object to construct a map of named design docs from a path containing js scripts.
 * It populates couchdb design documents from js files targeting Spidermonkey 1.8.5 
 * 
 * File paths like 
 * * designdocs/map/priority.js
 * * designdocs/reduce/priority.js`
 * * designdocs/update/handleSave.js`
 * ...are mapped to literal js strings containing function definitions...
 * * lowban.views.priority.map 
 * * lowban.views.priority.reduce
 * * lowban.updates.handleSave
 * 
 * Compatible files can be generated through babel, targeting browserlist `Firefox >= 4`
 */

class Loader{
  constructor({
    scriptRoot="../designdocs", 
    scriptExtension=".js"
  } = {}){
    this.scriptRoot = path.resolve(__dirname,scriptRoot)
    this.scriptExtension = scriptExtension
  }

  locateScript(scriptType, scriptId){
    return `${this.scriptRoot}/${scriptType}/${scriptId}${this.scriptExtension}`
  }

  readScriptPath(scriptPath){
    return fs.readFileSync(scriptPath, "utf8")
  }

  readScript(scriptType, scriptId) {
    return this.readScriptPath(this.locateScript(scriptType, scriptId))
  }

  evalScript(scriptType, scriptId, context) {
    const scriptPath = this.locateScript(scriptType, scriptId)
    const scriptSource = this.readScriptPath(scriptPath)
    return nodeEval(scriptSource, scriptPath, context)
  }

  getScriptIds(scriptType) {
    return glob.sync(`${this.scriptRoot}/${scriptType}/*` + this.scriptExtension).map(filePath => path.basename(filePath, this.scriptExtension))
  }
    
  loadDesignDocs() {

    const mapIds = this.getScriptIds("map")
    const reduceIds = this.getScriptIds("reduce")
    const updateIds = this.getScriptIds("update")

    const orphanedReducers = reduceIds.filter( id => !mapIds.includes(id))
    if(orphanedReducers.length > 0){
      throw `No map function for ${orphanedReducers}`
    }

    const views = mapIds.length ? {views:{
      //merge each view's map (and optional reduce)
      ...Object.assign(...mapIds.map( viewId => ({
        [viewId]: {
          map:this.readScript("map", viewId), //view map is required
          ...reduceIds.includes(viewId) //view reduce is optional
            ? { reduce:this.readScript("reduce", viewId) }
            : null
        }
      })))
    }} : null

    const updates = updateIds.length ? { updates:{
      //merge updates
      ...Object.assign(...updateIds.map( updateId => ({
        [updateId]:this.readScript("update", updateId)
      })))            
    }}: null

    return [
      {
        _id:"_design/lowban",
        ...views,
        ...updates,
      }
    ]    
  }
}

module.exports = {
  Loader
}