How do I check if an object has a key in JavaScript? [duplicate]
This question already has answers here: How do I check if an object has a specific property in JavaScript? (31 answers) Closed 8 years ago.
Which is the right thing to do?
if (myObj['key'] == undefined)
or
if (myObj['key'] == null)
or
if (myObj['key'])
!!myObj.key which returns true (if in) and false (if not).
const user = { name: "John", admin: false }; !!user.name will return true. But !!user.admin will return false even though the 'admin' key exists
Try the JavaScript in operator.
if ('key' in myObj)
And the inverse.
if (!('key' in myObj))
Be careful! The in operator matches all object keys, including those in the object's prototype chain.
Use myObj.hasOwnProperty('key') to check an object's own keys and will only return true if key is available on myObj directly:
myObj.hasOwnProperty('key')
Unless you have a specific reason to use the in operator, using myObj.hasOwnProperty('key') produces the result most code is looking for.
You should use hasOwnProperty. For example:
myObj.hasOwnProperty('myKey');
Note: If you are using ESLint, the above may give you an error for violating the no-prototype-builtins rule, in that case the workaround is as below:
Object.prototype.hasOwnProperty.call(myObj, 'myKey');
has**Own**Property ?
Do not access Object.prototype method 'hasOwnProperty' from target object.
{}.hasOwnProperty.call(object, "key")
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