JS: Check Property Existence

Check If a Object Has Own Property

obj.hasOwnProperty(key)

[see JS: Object.prototype.hasOwnProperty]

Check If a Property is in Prototype Chain

To check if a property key is in a object obj's prototype chain (including if it's its own property), use one of:

• key in obj [see JS: “in” Operator]
• Reflect.has ( obj, key ) [see JS: Reflect.has]