What is the rationale behind TypeScript permitting undefined methods?

Currently, I am working on a presentation for my development team about TypeScript. I want to demonstrate the importance of type checking through examples, but I'm stumped as to why this particular piece of code is not throwing a compile-time error when it reaches the ".notafunction" call. Any ideas?

/// <reference path="typings/jquery/jquery.d.ts" />

function greeting(person : any) {
    return "Hello " + person + "!";
}

$(document).ready(function () {
    var user = ".Net Development Team";

    $("#greeting-header").notafunction(greeting(user));

});

Answer №1

It seems like the issue is related to TypeScript and Typings within VS2017.

The file script/typings/jquery/jquery.d.ts that comes with

Install-Package jquery.TypeScript.DefinitelyTyped -Version 3.1.2

differs from the node_modules\@types\jquery\index.d.ts installed using

npm install --save @types/jquery

After installing typescript outside of VS2017, I encountered the same JQuery error. However, switching back to typings resolved the issue.

Your insights are greatly appreciated.

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