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  • Looking for Champion: Null Coalescing (??) and Null Conditional Member Access (?.) operators

Looking for Champion: Null Coalescing (??) and Null Conditional Member Access (?.) operators

# Arash Motamedi (6 years ago)

I’d like to propose two new operators that I’ve appreciated using in C#, with appropriate modifications for Ecmascript.

?? Null-Coalescing Operator

The ?? operator is called the null-coalescing operator. It returns the

left-hand operand if the operand is not null or undefined; otherwise it returns the right hand operand. (modified excerpt from C# definition, here docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operator .)

Examples:

let u = undefined; let nu = u ?? 0; // nu = (u !== undefined && u !== null) ? u : 0

let n = null; let nn = n ?? "Default"; // nn = (n !== undefined && n !== null) ? n : "Default";

let p = someObj.someProp ?? "Hello"; // p = (someObj.someProp !== undefined && someObj.someProp !== null) ? someObj.someProp : "Hello";

The ?? operator allows for a very terse syntactic representation of a rather common statement, and its value becomes very clear when evaluating and accessing properties on objects, as illustrated in the 3rd example above. For credit, comparison, and further details, please review the C# null coalescing operator information here docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operator .

?. Null Conditional Member Access and ?[ Null Conditional Index Access

Used to test for null or undefined before performing a member access (?.)

or index (?[) operation. (modified excerpt from C# definition here docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators .)

Examples:

let n = null; let nn = n?.name; // nn = (n.name !== null && u.name !== undefined) ? u.name : u.name;

let p = {name: "John"}; let l = p.lastName?.length; // l = (u.lastName !== null && u.lastName !== undefined) ? u.lastName.length : u.lastName;

The ?. and ?[ operators allow for graceful access (as opposed to null/undefined reference errors) to object members, and are particularly useful when used in a chained manner. For credit, comparison, and further details, please review the C# null conditional member access operator information here docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators .

Combining the above operators can enable very concise syntax for checking against null/undefined and providing default values in a graceful manner.

let lastNameLength = person.lastName?.length ?? 0; let cityToUppercase = person.address?.city?.toUpperCase() ?? "N/A";

Looking forward to working with the community and hopefully bringing these two operators to the language.

Best, Arash

# Claude Pache (6 years ago)

There are already official proposals for those. See:

tc39/proposals, tc39/proposals

and search for “Nullish coalescing Operator” for the first of your suggestions and “Optional Chaining” for the second one.

# Arash Motamedi (6 years ago)

Excellent! Thanks so much for the pointers. These will be great syntactic improvements.

# Ahmad Bamieh (6 years ago)

Thank you for this detailed write up! I believe you can help in the existing proposals!

Cheers! Ahmad Bamieh,