xilix / uo.js

aim to solve "Cannot read property wathever of undefined" runtime errors in javascript

UO

Aims to solve the problem of the error Cannot read property wathever of undefined. When there is a complex object such us:

  let person = {
    name: 'Jhon',
    lastname: 'Smith',
    job: {
      name: 'butcher',
      salary: 20000,
      company: {
        name: 'meats && cows inc.',
        revenue: 30000000
      },
      perks: {
        insurance: [
          {
            name: 'health care insurance',
            amount: 1000
          },
          {
            name: 'travel insurance',
            amount: 500
          }
        ]
      }
    }
  };

if some operation over some nested key is need but we cannot asure that any of the parent keys are set up then is need to check all the parent keys in order to avoid a Cannot read property wathever of undefined runtime error:

var getJobInsurancesAmount = function (person) {
  if (
    person &&
    person.job &&
    person.job.perks &&
    person.job.perks.insurance
  ) {
    return person.job.perks.insurance.reduce((amount, insurance) => {
      return amount + insurance.amount;
    }, 0); 
  }
};

uo allows to safely get any nested value without having to check every key. This allows to simplify this kind of checks:

const uo = require('uo.js');

var getJobInsurancesAmount = function (person) {
  if (uo(person, 'job', 'perks', 'insurance')) {
    return person.job.perks.insurance.reduce((amount, insurance) => {
      return amount + insurance.amount;
    }, 0); 
  }
};

also it can be used to safe get some nested value, for example:

const uo = require('uo.js');

var getJobInsurancesAmount = function (person) {
    return (uo(person, 'job', 'perks', 'insurance') || [])
    .reduce((amount, insurance) => {
      return amount + insurance.amount;
    }, 0); 
  }
};

or

const uo = require('uo.js');

var getCompanyName = function (person) {
  return uo(person, 'job', 'company', 'name');// 'meats && cows inc.'
};

var getCarBrand = function (person) {
  return uo(person, 'job', 'car', 'brand');// undefined
};

Usage

Install dependency

npm install --save uo.js

require dependency

const uo = require('uo.js');

Warnings

Sometimes it may be better to have a runtime error when tring to access a property key of an undefined object following the principle of crash early but in other controlled situation it may be useful to be able to safely get this property. Use it wisely, you now better than anybody your code.