---
sourceDocument: Yokohama API Reference
sourceDocumentLink: https://servicenow-prod.fluidtopics.net/r/yokohama/api-reference

 Release :

    - yokohama

ft:locale :

    - en-US

ft:publication_title :

    - Yokohama API Reference

ft:clusterId :

    - crapiref

bundleId :

    - crapiref

workflow :

    - Creator


---

# JavaScript engine on the platform

# JavaScript engine on the platform {#ariaid-title1}

Release version: Yokohama  
Updated January 30, 2025  
![](https://www.servicenow.com/docs/portal-asset/ico-clock) 1 minute to read  
The JavaScript engine that evaluates server-side scripts supports the ECMAScript 2021
(ES12) standard.

No plugins or properties are required to install the new JavaScript engine.  
The benefits of the new engine are:

* Modern library code and scripting features, such as optional chaining, destructuring, const and let declarations, and arrow functions
* Follows standard ECMAScript 2021 behavior
{#c_JS_engine_upgrade__ul_rnr_qkq_tv}

## What to know {#c_JS_engine_upgrade__section_v1n_stp_jbb}

The JavaScript engine provides an improved environment for developing scripts.

* Beginning with the Xanadu release, when you create new scripts, ECMAScript 2021 (ES12) mode is turned on by default regardless of the JavaScript mode configured for the application.
* Beginning with the Tokyo release, new and existing scoped applications can run in ECMAScript 2021 (ES12) mode.
* Compatibility mode supports the legacy modifications to the legacy JavaScript engine.
* Legacy code continues to work.
{#c_JS_engine_upgrade__ul_nv4_rmq_tv}

You configure the mode that the JavaScript engine uses in the design and runtime settings for applications. Available modes are ECMAScript 2021 (ES12), ES5 Standards, and Compatibility.
* **[JavaScript modes](https://servicenow-prod.fluidtopics.net/4PxNYtigt6VDcJsYahgc4Q)**   
  JavaScript mode is a design and runtime setting for custom applications and scripts. To support existing server-side scripts and new scripts developed to the ECMAScript 2021 standard, the JavaScript engine has three modes: ECMAScript 2021 (ES12), ES5 Standards, and Compatibility.
* **[JavaScript engine feature support](https://servicenow-prod.fluidtopics.net/Yjah1V6y8lh3R0HXOKclFQ)**   
  Compare ECMAScript features between the ECMAScript 2021 (ES12) and ES5 Standards JavaScript modes in Yokohama. Both modes support a subset of ECMAScript features.

**Related topics**   

* [Modify an app's settings in ServiceNow Studio](https://www.servicenow.com/docs/access?context=modify-an-apps-settings-in-servicenow-studio&version=yokohama&pubname=yokohama-application-development&ft:locale=en-US)