Sometimes in Javascript we have an object which we need to conform to a specific set of keys. This is possible through type enforcement in TypeScript, but if we want to do certain things if the keys don't exist, then we have to take a different approach. For example, suppose we are receiving the following object from an array, where , , and are all needed for an operation we want to complete. For example; firstName lastName age let obj = { firstName: Jack, lastName: Doe, age: 123 } console.log(`${obj.firstName} ${obj.lastName} is ${obj.age}`); If we are receiving our data in from an array, we could trust that those properties will be provided, but if the API ever changes we may face issues. The developers of the API may decide to remove or any other property, or maybe rename to . In the scenario, this will lead to keys becoming undefined. In the worst, it may result in an error and crash our application. obj age firstName first_name best To avoid this, we can check the object has the keys we . require How to Check if Object Contains all Keys in Array The solution to this problem uses . is an array method which checks every element in an array, and performs a logical check on them. If all return true, then the method returns true. every() every() every() To check if an object contains all keys in an array, we just use on an array of all the keys we want to check. That way we can logically check each element exists, and then do something else if it's false, preventing us from encountering any errors: every() let requiredKeys = [ 'firstName', 'lastName', 'age' ] let obj = { firstName: Jack, lastName: Doe, age: 123 } let checkAllKeys = requiredKeys.every((i) => obj.hasOwnProperty(i)); if(checkAllKeys) { console.log(`${obj.firstName} ${obj.lastName} is ${obj.age}`); } else { console.log('The API does not have all the keys required. Please check API and configuration') } Here we create an array of our - , , and . We then use to go through each item in that array. In , we run a function - here, is the the current item being looped through. If has the property , then will return true for that specific item. required keys firstName lastName age every() every() i obj i every() If every item returns true, then returns true overall. Otherwise it will return false. As such, if is true, we can be sure it has all the keys we need. Otherwise, we can do something else - like console log an error. every checkAllKeys
