JavaScript - find all available functions and properties in an object

2 minute read

The following three functions are very useful on inspecting methods and properties in any Javascrip object.
Github code: https://github.com/nsclass/describe-javascript-object-methods/blob/master/list-object-methods.js

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const getArgs = func => {
  // First match everything inside the function argument parens.
  let matchedItems = func.toString().match(/function\s.*?\(([^)]*)\)/)
  if (matchedItems && matchedItems.length > 0) {
    let args = matchedItems[1].trim()
    if (args.length > 0) {
      // Split the arguments string into an array comma delimited.
      return args.split(',').map( arg => {
        // Ensure no inline comments are parsed and trim the whitespace.
        return arg.replace(/\/\*.*\*\//, '').trim()
      })
    }
  }
  return "no args"
}
const getMethods = (obj) => {
  return Object.entries(obj)
  .filter(([key, value]) => typeof obj[key] === 'function')
  .map(([key, value]) => `${key}: ${getArgs(value)}`)
  .sort((x, y) => {
    let strX = x.toString()
    let strY = y.toString()
    return strX.localeCompare(strY)
  })
}
const getProperties = obj => {
  return Object.getOwnPropertyNames(obj)
  .filter(item => typeof obj[item] !== 'function')
}

For instance, we can list all available functions and each function's arguemnts in fs node module.

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const fs = require('fs)
getMethods(fs)

Results

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[ '_debugEnd: no args',
  '_debugProcess: no args',
  '_fatalException: no args',
  '_getActiveHandles: no args',
  '_getActiveRequests: no args',
  '_kill: no args',
  '_linkedBinding: module',
  '_rawDebug: no args',
  '_startProfilerIdleNotifier: no args',
  '_stopProfilerIdleNotifier: no args',
  '_tickCallback: no args',
  'abort: no args',
  'activateUvLoop: no args',
  'assert: ...args',
  'atomBinding: name',
  'binding: module',
  'chdir: ...args',
  'cpuUsage: prevValue',
  'crash: no args',
  'cwd: no args',
  'dlopen: no args',
  'emitWarning: no args',
  'exit: no args',
  'getCPUUsage: no args',
  'getCreationTime: no args',
  'getegid: no args',
  'geteuid: no args',
  'getgid: no args',
  'getgroups: no args',
  'getHeapStatistics: no args',
  'getIOCounters: no args',
  'getRenderProcessPreferences: no args',
  'getSystemMemoryInfo: no args',
  'getuid: no args',
  'hang: no args',
  'hasUncaughtExceptionCaptureCallback: no args',
  'hrtime: time',
  'initgroups: ...args',
  'kill: no args',
  'log: no args',
  'memoryUsage: no args',
  'NativeModule: id',
  'nextTick: no args',
  'openStdin: no args',
  'reallyExit: no args',
  'setegid: ...args',
  'seteuid: ...args',
  'setFdLimit: no args',
  'setgid: ...args',
  'setgroups: ...args',
  'setuid: ...args',
  'setUncaughtExceptionCaptureCallback: no args',
  'takeHeapSnapshot: no args',
  'umask: ...args',
  'uptime: no args' ]

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