检查嵌套对象中是否存在对象成员

Question

Is there a simpler way than using ___ in object to check the existence of each level of an object to check the existence of a single member?

More concisely: How can I check if someObject.member.member.member.value exists?

Answer 1

In general, you can use if(property in object) , but this would be still cumbersome for nested members.

You could write a function:

function test(obj, prop) {
    var parts = prop.split('.');
    for(var i = 0, l = parts.length; i < l; i++) {
        var part = parts[i];
        if(obj !== null && typeof obj === "object" && part in obj) {
            obj = obj[part];
        }
        else {
            return false;
        }
    }
    return true;
}

test(someObject, 'member.member.member.value');

DEMO

Answer 2

You could also try/catch TypeError?

try {
  console.log(someObject.member.member.member.value);
} catch(e) {
  if (e instanceof TypeError) {
    console.log("Couldn't access someObject.member.member.member.value");
    console.log(someObject);
  }
}

Answer 3

Here's one way: http://jsfiddle.net/9McHq/

var result = ((((someObject || {}).member || {}).member || {}).member || {}).value;

alert( result );

Answer 4

Check out lodash-deep's deepHas https://github.com/marklagendijk/lodash-deep#_deephascollection-propertypath

And this too https://github.com/danielstjules/hoops

Answer 5

Theres a safeRead function defined here on thecodeabode which allows a safeRead of nested properties ie

safeRead(foo, 'bar', 'jim', 'jam');

if any of the properties are null or undefined a blank string is returned - useful for formatting / string interpolation

Answer 6

Something like (warning: untested code ahead)

var testProperty = function(obj, proplist) {
   for (var i=0; i < proplist.length; i++) {
      if (obj.hasOwnProperty(proplist[i])) {
         obj = obj[proplist[i]];
      } else {
        return false;
      }
   }
   return true;
}

Answer 7

if (someObject.member && someObject.member.member &&
    someObject.member.member.member && someObject.member.member.member.value) ...

or similarly:

var val = foo.bar && foo.bar.jim && foo.bar.jim.jam && foo.bar.jim.jam.value;

This will not 'work' if any particular value happens to be null , false , 0 , or "" (an empty string), but with the possible exception of the final value, this seems unlikely to be the case.

Also, note that typeof ____ !== "undefined" is not the correct test to see if an object has a property. Instead you should use ___ in object , eg if ("member" in someObject) . This is because you can set a property to an explicit value of undefined , which is different from removing it with delete someObject.member .

Answer 8

If you can use lodash library, it has a very elegant solution, hasIn .

_.hasIn(someObject, 'member.level1.level2.level3');

for example,

var obj = {'x': 999, 'a': {'b': {'c': 123, 'd': 234}}}
// => undefined

_.hasIn(obj, 'x')
// => true

_.hasIn(obj, 'a.b.d')
// => true

_.hasIn(obj, 'a.b.e')
// => false