How to Check for the Existence of Nested JavaScript Object Key

To check for the existence of a property in nested objects, you should do it step by step to avoid a TypeError. It will be thrown if at least one member is null or undefined and you try to access a property on it.

There are two ways to avoid it. Either you can catch the exception using a try-catch block, or create a function to test the existence of multiple levels like this:

Check for the existence of nested javascript object key

Using ES6 features can make the function even shorter:

Check for the existence of nested javascript object key

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

To get the nested property value and also check its existence, use the following one-liner:

Get the nested property value and also check javascript

You can also use the optional chaining operator to access deeply nested properties, by using the token ?.:

Check for the existence of nested javascript object key

const value = obj?.level1?.level2?.level3;

If any of the accessed levels is null or undefined, the expression will resolve to undefined.

The operator also handles method calls safely:

Check for the existence of nested javascript object key

obj?.level1?.method?.();

The above expression produces undefined if obj, obj.level1, or obj.level1.method are null or undefined; otherwise, it will call the function.

The optional chaining operator

The optional chaining operator (?.) is a standard feature in ES2020. It permits reading the value of a property that is located deep in a chain of connected objects without having to expressly validate that each reference is valid. The ?. operator allows it to short-circuit if a reference evaluates to null or undefined. When used with function calls, it returns undefined if the function does not exist.