I am writing some type check functions. I want:   isInteger isFloat   While writing isInteger, I noticed that isInteger(1.0) returns true. I want this to return false.  My function is like this:  function isInteger(value) {     return typeof value ==...
I have a value that comes from a select input and is of type string, however I want to pass it into a function (updateLanguage) that receives as argument a string enum with a type alias (Language).   The problem I'm facing is that Flow only allow...
Update: These checks are meant for compile time, not at runtime. In my example, the failed cases are all caught at compile time, and I'm expecting similar behaviour for the other should-fail cases.   Suppose I'm writing a table-like class whe...
I understand why you need to use Object.prototype.toString() or String() for typechecking arrays, but isn't typeof sufficient for typechecking functions and strings? For example the polyfill on MDN for Array.isArray uses:  Object.prototype.toStri...
My team works on a relatively large NodeJS project, written in ES6, transpiled by babel, and then deployed as AWS lambdas with Serverless. This project is focused around consuming, mapping/transforming, and outputting one specific object type, which...
I have a function in my component which will access the router parameters.  import { withRouter } from 'react-router-dom'; import type { Match } from 'react-router-dom';  @withRouter export default class UserDetails extends Component...
In the following code, I am trying to work with an instance of class Test after a type check.  main.ts  class Test {     x: number = 0;     test() {} }  let t1: Test | number = new Test();  if (t1 instanceof Test) {     console.log(t1.x); // works...
I expected Closure Compiler to warn on all the lines below, but only 3) shows up as a problem.  Type Checking Array Contents with Closure-Compiler touches on this same point, but my question is, given these limitations, what benefits are realized fro...
Let's say I have this type  type Status = "draft" | "validated" | "private" | "available" | "archived";   I'm instantiating objects that map this enum type to a string:  const statusNameMap: { [Status]:...
I sometimes run into the situation that I have a JavaScript object of unknown type. Then I perform a type check in script and call appropriate functions depending on the detected type. e.g. like this  /**  * @param {!Array} aArray my array  */ functi...

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