JavaScript, elegant way to check nested object properties for null/undefined

Well, javascript has try-catch. Depending on what you actually need to do (i.e. what your else statement would look like if it's undefined), that may be what you want.

example:

try {
   user.loc.lat.doSomething();
} catch(error) {
   //report
}

You can combine the checks using lazy and:

if(user.loc && user.loc.lat) { ...

Or, you use CoffeeScript. And ES2020 has new syntax ( Nullish coalescing Operator ).

user.loc?.lat?. '...'

which would run the checks for loc property and safeguard against empty objects.

Try this if(user && user.loc && user.loc.lat) {...}

You can check value of null and undefined using typeof

If .loc has value false than you can try

if(user && user.loc && typeof(user.loc)!=="undefined"){...}

If you have a huge nested object than have a look at

Source.

function checkNested(obj /*, level1, level2, ... levelN*/) {
  var args = Array.prototype.slice.call(arguments),
      obj = args.shift();

  for (var i = 0; i < args.length; i++) {
    if (!obj.hasOwnProperty(args[i])) {
      return false;
    }
    obj = obj[args[i]];
  }
  return true;
}

var test = {level1:{level2:{level3:'level3'}} };

checkNested(test, 'level1', 'level2', 'level3'); // true
checkNested(test, 'level1', 'level2', 'foo'); // false

Update: Try lodash.get

You can use an utility function like this:

get = function(obj, key) {
    return key.split(".").reduce(function(o, x) {
        return (typeof o == "undefined" || o === null) ? o : o[x];
    }, obj);
}

Usage:

 get(user, 'loc.lat')     // 50
 get(user, 'loc.foo.bar') // undefined

Or, to check only if a property exists, without getting its value:

has = function(obj, key) {
    return key.split(".").every(function(x) {
        if(typeof obj != "object" || obj === null || ! x in obj)
            return false;
        obj = obj[x];
        return true;
    });
}

if(has(user, 'loc.lat')) ...