> For the complete documentation index, see [llms.txt](https://guide-angular.wishtack.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://guide-angular.wishtack.io/typescript/de-lecmascript-au-typescript.md).

# De l'ECMAScript au TypeScript

L'ECMAScript est quasiment du TypeScript valide étant donné que le typage est optionnel.

Il est donc facile de migrer progressivement de l'ECMAScript vers le TypeScript.

## Les Propriétés

L'un des principaux changements empêchant l'ECMAScript d'être du TypeScript valide est la nécessité de déclarer les propriétés d'une classe.

En renommant simplement le fichier JavaScript en `.ts`, l'IDE commence à se plaindre.

![](/files/-LAJ7b2WhyAQDlfH6Zoj)

Le compilateur TypeScript (`tsc`) est également mécontent.

```bash
$ tsc customer.ts
customer.ts(11,18): error TS2339: Property 'firstName' does not exist on type 'Customer'.
customer.ts(12,18): error TS2339: Property 'lastName' does not exist on type 'Customer'.
```

Le minimum syndical est donc de déclarer ces propriétés.

```typescript
class Customer {

    firstName;
    lastName;

    constructor(firstName, lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

}
```

{% hint style="success" %}
La bonne pratique est de déclarer les propriétés avant le constructeur.
{% endhint %}


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://guide-angular.wishtack.io/typescript/de-lecmascript-au-typescript.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.