---
sourceDocument: Yokohama Build or modify applications
sourceDocumentLink: https://servicenow-prod.fluidtopics.net/r/yokohama/application-development

 Release :

    - yokohama

ft:locale :

    - en-US

ft:publication_title :

    - Yokohama Build or modify applications

ft:clusterId :

    - cadev

bundleId :

    - cadev

workflow :

    - Development, Data, and Analytics


---

# 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/73pe2KxgXAXTtXOR_hUYAw)**   
  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/LhzkMv4D1uJmzKq6WMM7hQ)**   
  Compare ECMAScript features between the ECMAScript 2021 (ES12) and ES5 Standards JavaScript modes in Yokohama. Both modes support a subset of ECMAScript features.

**Related tasks**   

* [Modify an app's settings in ServiceNow Studio](https://servicenow-prod.fluidtopics.net/TQMgCWgaqDDz__XbfYicVQ "Adjust an app's settings in ServiceNow Studio using the full platform app record in app settings. Change the name, description, or other metadata associated with the app, and view all related links associated to the application.")