Trouble with Javascript object manipulation

Question

Let's say I have a JavaScript object that is made up of several key/value pairs of string keys and JavaScript objects.

var obList = { key:{..}, key2:{..}, key3:{..}, ... }

And I construct a new set, obList2

var obList2 = { key:{..}, key2:{..}, key3:{..}, ... }

I want to write a function that modifies obList based on obList2. The initial step I'm having trouble with is removing all objects in obList that have a key not present in obList2. Any thoughts/implementation of this would be v helpful. Thank you!

Answer 1

You can loop over objects using a for .. in loop and check if properties exist using Object.hasOwnProperty().

Example:

for (var prop in obList) {
    if (obList.hasOwnProperty(prop) && !obList2.hasOwnProperty(prop)) {
        delete obList[prop];
    }
}

The first condition is a safeguard against modifications to Object.prototype and the second checks to see if the property isn't present on the second object.

Answer 2

Basic element for your code: ability to check if a particular key is missing from an object. Here's how you'd do it:

if (window.bla === undefined) { 
  console.log("Key bla is missing!")
}