declare function require(moduleNames: string[], onLoad: (...args: any[]) => void): void; import * as Zip from "./ZipCodeValidator"; if (needZipValidation) { require(["./ZipCodeValidator"], (ZipCodeValidator: typeof Zip) => { let validator = new ZipCodeValidator.ZipCodeValidator(); if (validator.isAcceptable("...")) { /* ... */ } }); }