There are times when I iterate through JSON string objects using the following code:
for(var i in JSONObject){
....
}
Is it necessary to use .hasOwnProperty here? My understanding is that since JSON is not inherited from a parent object, it is safe to assume that all its properties are its own.
JSON is often assumed to have its own properties since it isn't extended from a parent object, but that assumption is not entirely correct.
Contrary to popular belief, unless an object was created using Object.create(null), it inherits the Object.prototype in its prototype chain. This means that properties like hasOwnProperty and toString are actually defined in the prototype chain of most objects, including those created from JSON using JSON.parse. However, standard properties defined on Object.prototype are not enumerable, so they will not show up in a for..in loop.
So, the decision of whether to use hasOwnProperty depends on the context.
If you can be certain that no code (whether your own or third-party) adds enumerable properties to Object.prototype, then there may be no need to use hasOwnProperty in the loop.
However, if there is any uncertainty about potential additions to Object.prototype, it might be safer to use hasOwnProperty as a precaution. Ideally, avoiding extensions of Object.prototype with enumerable properties and being cautious with third-party code is recommended.
Related:
After conducting some tests, I discovered that JSON strings do not transmit inherited properties. Imagine you receive an API response from an endpoint and when you prettify it, it looks like this:
{
"one": "blue",
"two": "watermelon",
"three": "lalal",
"four": "value"
}
When you iterate over the parsed value of the above using a for(var i in JSONObject) loop, you will only find four properties associated with the object unless you have explicitly attached any properties to the parent Object literal (Object.prototype) in your current environment.
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