I think the answer is that humans are still smarter than typecheckers. I know that's not satisfying, but it's true. The typechecker typically uses just conditional statements to determine whether something can be null. But this code example feels a little contrived. I would probably restructure the code like this:
var myArray: (Array<any> | null);
if (cnd) {
elt.key = value;
myArray = [elt];
} else {
myArray = null;
}
This removes those two oddities.
Answer from jack on Stack OverflowBobby Hadz
bobbyhadz.com › blog › typescript-question-mark-dot
What is the ?. operator (optional chaining) in TypeScript | bobbyhadz
If the property is populated on the object, the optional chaining operator (?.) returns the specified value in the array.
Top answer 1 of 2
2
I think the answer is that humans are still smarter than typecheckers. I know that's not satisfying, but it's true. The typechecker typically uses just conditional statements to determine whether something can be null. But this code example feels a little contrived. I would probably restructure the code like this:
var myArray: (Array<any> | null);
if (cnd) {
elt.key = value;
myArray = [elt];
} else {
myArray = null;
}
This removes those two oddities.
2 of 2
0
For question 1, you can refer to this link
For question 2, just perform a check against null like this before accessing your object
if (obj !== null) {
obj.doSomeThing();
}
or just simply like the following if your object can be null or undefined. null and undefined are what are called falsy value, so when they are used in a boolean context, they are automatically coerced to false
if (obj) {
obj.doSomeThing();
}
Reddit
reddit.com › r/learnprogramming › is the question mark before accessing some property in typescript bad?
r/learnprogramming on Reddit: is the question mark before accessing some property in typescript bad?
December 20, 2022 -
I’m calling a rest api using react query and it’s returning me an array of objects. I have already defined the type for that object and i’m trying to transform that response array into something else using .map or .reduce.
I have the condition for isLoading or isIdle present. So i’m assuming that after that code block, the data would be present. Is my assumption flawed?
I’m using a ternary in my return jsx function and there’s no error on my end so far. So is the question mark bad?
Top answer 1 of 2
2
It's kind of hard to say without seeing any code. You have to remember the TS compiler only knows what you tell it, so unless the compiler knows that there will be data with the isIdle state and not the isLoading state, it might work more intuitively for you. Here's a quick example of something that changes types based on the loading state: type Stuff = { loading: true } | { loading: false, data: { foo: "string" } }; function fn(stuff: Stuff) { if (stuff.loading) { // Type error console.log(stuff.data); } if (!stuff.loading) { // All good console.log(stuff.data); } }
2 of 2
1
Can you share the code you are referring to? It'd help to clarify your question to get better answers.
TypeScript
typescriptlang.org › docs › handbook › release-notes › typescript-3-7.html
TypeScript: Documentation - TypeScript 3.7
At its core, optional chaining lets us write code where TypeScript can immediately stop running some expressions if we run into a null or undefined. The star of the show in optional chaining is the new ?. operator for optional property accesses.
Omarileon
omarileon.me › blog › typescript-double-question-mark
mari. | Demystifying TypeScript's Double Question Mark: Nullish Coalescing
January 25, 2024 - As well as the null coalescing operator, you might also find the less commonly used Nullish coalescing assignment operator used in TypeScript - double question marks followed by equals.
Graphite
graphite.com › guides › typescript-operators
Operators in TypeScript
The spread operator (...) allows an iterable such as an array or string to be expanded in places where zero or more arguments (for function calls) or elements (for array literals) are expected. ... The in operator returns true if the specified property is contained in the specified object or its prototype chain. ... In TypeScript, the question mark is used in two contexts.
Educative
educative.io › answers › how-to-use-a-question-mark-in-typescript-variables
How to use a question mark in TypeScript variables
The question mark in typescript can be used to mention that a variable is optional or to pre-check if a member variable is present for an object.
Gyata
gyata.ai › typescript › typescript-question-mark-operator
TypeScript Question Mark Operator | Gyata - Learn about AI, Education & Technology
The TypeScript Question Mark Operator is a powerful tool that can simplify and improve your code. It provides a safe way to access nested object properties, call functions, and access array indices. However, it should be used wisely and sparingly, keeping in mind its short-circuiting behavior ...
MDN Web Docs
developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › Optional_chaining
Optional chaining (?.) - JavaScript | MDN
You can also use the optional chaining operator with bracket notation, which allows passing an expression as the property name: ... This is particularly useful for arrays, since array indices must be accessed with square brackets.
Delft Stack
delftstack.com › home › howto › typescript › question mark in typescript
Question Mark Operator in TypeScript | Delft Stack
January 30, 2023 - The question mark or ? has relieved the users by defining optional parameters. Moreover, the ? operator can also act as a shorthand for checking if a certain attribute of an object is null or undefined.
Medium
medium.com › totally-typescript › what-does-the-question-mark-dot-mean-in-javascript-or-typescript-9d7d744f6077
What Does the ?. Question Mark Dot Mean in JavaScript or TypeScript? | by Dr. Derek Austin 🥳 | Totally TypeScript | Medium
May 16, 2023 - What Does the ?. Question Mark Dot Mean in JavaScript or TypeScript? Unraveling the mystery of the ?. optional chaining operator with practical examples Introduction: Optional Chaining in JS / TS …
Reddit
reddit.com › r/learnjavascript › what does the question mark in the context of this expression mean: array?.length
r/learnjavascript on Reddit: What does the question mark in the context of this expression mean: array?.length
October 10, 2021 -
To clarify I am referring to the first question mark, array?.length. I saw this somewhere and can't recall what it does.
const array = [1,2,3] array?.length > 0 ? 'Array contains elements' : 'No elements within array';
Top answer 1 of 8
76
This is known as optional chaining. If array exists it will access the length property otherwise it will evaluate to undefined. This is used to prevent run time errors, 'Cannot read property length of undefined'
2 of 8
35
Just to add to the answer by u/rossmci90 , this is used when array is created somewhere else in your program, and you cannot be certain that is actually refers to an array (or indeed any object) - i.e. there's a possibility array is undefined. It's shorthand for (roughly) array && array.length > 0 ... Or if(typeof(array) != 'undefined') { if(array.length > 0) ... If you didn't do one of these things, you'd get an error saying that you cannot read "length" of undefined. Obviously, if you have two or three of these things in sequence people[2].identity.name Then if statements get very messy and the intent of the code gets lost in the blocks. But people[2]?.identity?.name Is nearly the same thing, visually, and the intent is retained.
EDUCBA
educba.com › home › software development › software development tutorials › typescript tutorial › typescript question mark
TypeScript Question Mark | Complete Guide to TypeScript Question Mark
April 11, 2023 - As it is supported with TypeScript 3.7 version, called Optional chaining. This variant, the existential operator ‘?.’ is used to soak up all the null references. With this, we shall conclude the topic ‘TypeScript question mark’. We have seen what TypeScript question mark is and its syntax.
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GeeksforGeeks
geeksforgeeks.org › why-use-question-mark-in-typescript-variable
Why use Question Mark in TypeScript Variable? - GeeksforGeeks
October 14, 2024 - The question mark in TypeScript is used to mark a variable as optional, allowing it to be omitted or set to undefined. This is commonly used in object properties and function parameters, enhancing flexibility by making variables non-mandatory.
freeCodeCamp
freecodecamp.org › news › how-the-question-mark-works-in-javascript
How the Question Mark (?) Operator Works in JavaScript
February 3, 2021 - By Nishant Kumar The conditional or question mark operator, represented by a ?, is one of the most powerful features in JavaScript. The ? operator is used in conditional statements, and when paired with a :, can function as a compact alternative ...
DEV Community
dev.to › danywalls › simplify-your-typescript-code-with-optional-chaining-and-nullish-coalescing-37on
Simplify Your Typescript Code with Optional Chaining and Nullish Coalescing - DEV Community
May 23, 2023 - The double question mark (??) checks if the left-hand side value is nullish (null or undefined) and provides the right-hand side value as the default if needed. Nullish coalescing ensures that we always have a valid jersey number, even if it's ...
Becomebetterprogrammer
becomebetterprogrammer.com › typescript-question-mark
Understanding the Question Mark (?:) in TypeScript - Become A Better Programmer
April 25, 2022 - In the initial example, we noticed the usage of the question mark with a colon (?:) when defining the properties of an interface. In a similar way, we can do so this when defining a class. class Car { id: string; brand: string; model: string; year: number; price?: number; } This gives the flexibility to not having the need to provide values to all properties of a class. We can also define optional parameters when creating functions in TypeScript.
egghead.io
egghead.io › lessons › typescript-use-the-optional-chaining-operator-in-typescript
Use the Optional Chaining Operator in TypeScript | egghead.io
[5:29] If you were to work with arrays, you can use the syntax to access array indices, for example. Finally, there's a third version of the optional chaining syntax. That's used for working with functions. To demonstrate the syntax, let me refactor our property to a method. Let's make sure this method is optional. [5:55] We can now call this function in our optional property chain by stating the name and then the syntax question mark dot, and parentheses for calling the function.
Published February 17, 2021
Medium
medium.com › @teamcode20233 › understanding-double-question-mark-operator-in-typescript-be869f210fe6
Understanding Double Question Mark Operator (??) in TypeScript | by Teamcode | Medium
July 3, 2023 - The syntax for using the double question mark operator is value1 ?? value2, where value1 is the expression to be evaluated and value2 is the fallback value to be used if value1 is null or undefined. This operator helps to simplify conditional checks and provides a more streamlined approach to handling nullish values in TypeScript code.
TypeScript
typescriptlang.org › docs › handbook › 2 › objects.html
TypeScript: Documentation - Object Types
In those cases, we can mark those properties as optional by adding a question mark (?) to the end of their names. ... In this example, both xPos and yPos are considered optional. We can choose to provide either of them, so every call above to paintShape is valid.