How to check if a key exists in a JavaScript object
Given a JavaScript object, you can check if a property key exists inside its properties using the in
operator.
Say you have a car
object:
const car = {
color: 'blue'
}
We can check if the color
property exists using this statement, that results to true
:
'color' in car
We can use this in a conditional:
if ('color' in car) {
}
Another way is to use the hasOwnProperty()
method of the object:
car.hasOwnProperty('color')
When inheritance is an important part of your applications structure, the difference is that in
will result true
even for properties inherited by parent objects. hasOwnProperty()
doesn’t. It will only return true
if the object has that property directly - not one of its ancestors.
I use a fallback mechanism when I want one property and fallback to a default value if that does not exist:
car.brand || 'Ford'
If the brand
property key does not exist on the object, this statement results to the Ford
string.
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