> 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/ecmascript-6+/compatibilite.md).
# Compatibilité
Comment faire tant que toutes les fonctionnalités ne sont pas disponibles sur nos navigateurs cibles ?
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## Transpilation
ECMAScript 5.1 est à l'ECMAScript moderne ce que l'assembleur est au C++.
Nous avons donc besoin de transpilateurs :
* Babel:
* TypeScript:
Mais cela n'est pas suffisant car la transpilation ne fait que convertir les nouvelles fonctionnalités syntaxiques.
## Polyfills
Nous avons besoin de compenser l'absence de certains objects, fonctions ou méthodes `customElements`, `fetch`, `Array.filter` sur certains navigateurs.
Pour remédier à cette limitation, nous utiliserons des librairies de polyfills. Ces librairies détectent l'absence des fonctionnalités et décident dans ce cas de les compenser avec une implémentation JavaScript.
Exemple :
```javascript
if (Array.prototype.first == null) {
Array.prototype.first = function () {
return this[0];
};
}
const valueList = [1, 2, 3];
console.log(valueList.first()); // 1
```
L'une des librairies de polyfills les plus populaires est **core-js** .
Ou encore : [https://polyfill.io](https://polyfill.io/v2/docs/).
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