In JavaScript, it's commonly seen as best practice to use === instead of ==, for obvious and well-known reasons. In TypeScript, which is one to be preferred? Is there even one which is preferable ...
Yes. As of TypeScript 3.7 (released on November 5, 2019), this feature is supported and is called Optional Chaining: 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. Refer to the TypeScript 3.7 ...
The ?? operator was added to TypeScript 3.7 back in November 2019. And more recently, the ?? operator was included in ES2020, which is supported by Node 14 (released in April 2020).
It tells TypeScript to leave the expressions result as it is and pass it to JavaScript. It allows the use of JavaScript semantics in TypeScript, such as using loose equality (with the convenience of omitting all the checks) or using the (loose) inequality comparisons.
How to correctly type Object.keys() lookup in a JavaScript project with TypeScript type-checking enabled? [duplicate] I am working in a JavaScript project with TypeScript type-checking enabled (using // @ts-check or equivalent). So even my .js files are validated strictly against TypeScript types. I have a JavaScript ... javascript typescript ...
export function foo(arg: string): arg is MyType { return ... } I haven't been able to search for is in either the docs or google, it's a pretty common word and shows up on basically every page. What does the keyword do in that context?
When creating or maintaining TypeScript definitions for pure JavaScript modules, interfaces should probably be used for everything that is a class in the original module; particularly examples like chai, where the modules are designed to be extended through plug-ins.
TypeScript won't warn that lastName is never assigned and assumes its value is a string, when in fact it's not there and so reading its value will result in undefined.
You can't get the results of the TypeScript type query operator at runtime, because the type system is erased at runtime. You need to give up on the typeof operator. What you can do is check the value of myfruit against the three known Fruit string literals... like, for example, this:
