Tracing module resolution As discussed earlier, the compiler can visit files outside the current folder when resolving a module. This can be hard when diagnosing why a module is not resolved, or is resolved to an incorrect definition. Enabling the compiler module resolution tracing using --traceResolution provides insight in what happened during the module resolution process. Let’s say we have a sample application that uses the typescript module. app.ts has an import like import * as ts from "t

Type Guards and Differentiating Types Union types are useful for modeling situations when values can overlap in the types they can take on. What happens when we need to know specifically whether we have a Fish? A common idiom in JavaScript to differentiate between two possible values is to check for the presence of a member. As we mentioned, you can only access members that are guaranteed to be in all the constituents of a union type. let pet = getSmallPet(); // Each of these property accesses

ES6 Modules TypeScript 1.5 supports ECMAScript 6 (ES6) modules. ES6 modules are effectively TypeScript external modules with a new syntax: ES6 modules are separately loaded source files that possibly import other modules and provide a number of externally accessible exports. ES6 modules feature several new export and import declarations. It is recommended that TypeScript libraries and applications be updated to use the new syntax, but this is not a requirement. The new ES6 module syntax coexist

React integration To use JSX with React you should use the React typings. These typings define the JSX namespace appropriately for use with React. /// <reference path="react.d.ts" /> interface Props { foo: string; } class MyComponent extends React.Component<Props, {}> { render() { return <span>{this.props.foo}</span> } } <MyComponent foo="bar" />; // ok <MyComponent foo={0} />; // error