Test for existence of nested JavaScript object key

You have to do it step by step if you don't want a TypeError because if one of the members is null or undefined, and you try to access a member, an exception will be thrown.

You can either simply catch the exception, or make a function to test the existence of multiple levels, something like this:

function checkNested(obj /*, level1, level2, ... levelN*/) {  var args = Array.prototype.slice.call(arguments, 1);  for (var i = 0; i < args.length; i++) {    if (!obj || !obj.hasOwnProperty(args[i])) {      return false;    }    obj = obj[args[i]];  }  return true;}var test = {level1:{level2:{level3:'level3'}} };checkNested(test, 'level1', 'level2', 'level3'); // truecheckNested(test, 'level1', 'level2', 'foo'); // false

ES6 UPDATE:

Here is a shorter version of the original function, using ES6 features and recursion (it's also in proper tail call form):

function checkNested(obj, level,  ...rest) {  if (obj === undefined) return false  if (rest.length == 0 && obj.hasOwnProperty(level)) return true  return checkNested(obj[level], ...rest)}

However, if you want to get the value of a nested property and not only check its existence, here is a simple one-line function:

function getNested(obj, ...args) {  return args.reduce((obj, level) => obj && obj[level], obj)}const test = { level1:{ level2:{ level3:'level3'} } };console.log(getNested(test, 'level1', 'level2', 'level3')); // 'level3'console.log(getNested(test, 'level1', 'level2', 'level3', 'length')); // 6console.log(getNested(test, 'level1', 'level2', 'foo')); // undefinedconsole.log(getNested(test, 'a', 'b')); // undefined