UDATE. See this new library providing functor and monad operators for plain callback-based functions that do not have the issues with theneables: https://github.com/dmitriz/cpsfy The JS Promise is neither a Functor nor an Applicative nor a Monad It is not a functor, because the composition preservation law (sending compositions of functions to compositions of their images) … Read more
main.ts import {Promise} from ‘es6-promise’; const p: Promise<string> = new Promise ( (resolve: (str: string)=>void, reject: (str: string)=>void) => { const a: string = “hello from Promise”; resolve(a); } ); p.then((st) => { console.log(st); }); tsconfig.json { “compilerOptions”: { “target”: “es3”, “module”: “commonjs”, “declaration”: false, “noImplicitAny”: false, “noLib”: false }, “filesGlob”: [ “./**/*.ts”, “!./node_modules/**/*.ts” ], … Read more
For TypeScript 3.3.3, just add es2018.promise to your tsconfig.json – compilerOptions.lib config like this: “lib”: [“es2015”, “es2016”, “dom”, “es2018.promise”] If you use vscode, maybe you should reload window after adding this option to your tsconfig.json file
Yes, it most definitely should. A string is not an error, when you have errors usually it means something went wrong which means you’d really enjoy a good stack trace. No error – no stack trace. Just like with try/catch, if you add .catch to a thrown rejection, you want to be able to log … Read more
Comments First off, running promises inside of a .then() handler and NOT returning those promises from the .then() callback creates a completely new unattached promise sequence that is not synchronized with the parent promises in any way. Usually, this is a bug and, in fact, some promise engines actually warn when you do that because … Read more
Jest Mock Functions Mock functions are also known as “spies”, because they let you spy on the behavior of a function that is called indirectly by some other code, rather than just testing the output. You can create a mock function with jest.fn(). Check the documentation for jest.fn() Returns a new, unused mock function. Optionally … Read more
1) Return something from your asyncExample function const asyncExample = async () => { const result = await axios(users) return result } 2) Call that function and handle its returned Promise: ;(async () => { const users = await asyncExample() console.log(users) })() Here’s why should you handle it like this: You can’t do top-level await … Read more
The types for Promise.allSettled() were only merged in January, and will apparently be released in TypeScript 3.8. As an interim solution, you can declare a mock-ish type for the function yourself: declare interface PromiseConstructor { allSettled(promises: Array<Promise<any>>): Promise<Array<{status: ‘fulfilled’ | ‘rejected’, value?: any, reason?: any}>>; }
Promise.all() will be helpful here: var promises = []; array.forEach(function(element) { promises.push( developer.getResources(element) .then((data) = > { name = data.items[0]; return developer.getResourceContent(element, file); }) .then((response) = > { fileContent = atob(response.content); self.files.push({ fileName: fileName, fileType: fileType, content: fileContent }); }).catch ((error) = > { console.log(‘Error: ‘, error); }) ); }); Promise.all(promises).then(() => self.resultingFunction(self.files) ); This … Read more
Let’s say that throwing inside then() callback rejects the result promise with a failure, and returning from then() callback fulfills the result promise with a success value. let p2 = p1.then(() => { throw new Error(‘lol’) }) // p2 was rejected with Error(‘lol’) let p3 = p1.then(() => { return 42 }) // p3 was … Read more