To automatically add properties to an object that is undefined with JavaScript, we can use the hasOwnProperty method to check if a property exists.
It’ll return true if it exists and false otherwise.
If it returns false , then we can set the property value to the value we want.
For instance, we can write:
const test = {}
if (!test.hasOwnProperty('hello')) {
test.hello = {};
}
test.hello.world = "Hello World!"
We have the test object that we want to add the hello property to if it doesn’t exist.
We check that it doesn’t exist with !test.hasOwnProperty(‘hello’) .
And if that’s true , we set test.hello to an empty object.
Then we set test.hello.world to “Hello World!” .
The hasOwnProperty method can be overridden easily since it’s inherited from the Object constructor.
Therefore to make sure we always call the right hasOwnProperty method, we can write:
const test = {}
if (!Object.prototype.hasOwnProperty.call(test, 'hello')) {
test.hello = {};
}
test.hello.world = "Hello World!"
We call Object.prototype.hasOwnProperty.call with test to do the same thing as test.hasOwnProperty , but we make sure that we always call the right one from the Object constructor.
