JavaScript modes

  • Release version: Australia
  • Updated March 12, 2026
  • 2 minutes to read
    • Summarize
    Summarized using AI
    This content was generated using new OpenAI-powered functionality. Results are provided on an as is basis and are not guaranteed to be accurate or complete.

    Summary of JavaScript Modes

    JavaScript modes define the design and runtime settings for applications and scripts, impacting which JavaScript features are available. The three modes are: ECMAScript 2021 (ES12), ES5 Standards, and Compatibility. Default settings are ECMAScript 2021 (ES12) for new scoped applications and ES5 Standards for new global applications.

    Show full answer Show less

    Key Features

    • ECMAScript 2021 (ES12) Mode: Default for new scoped applications, supporting modern syntax and features like default function parameters, rest parameters, arrow functions, and optional chaining. Legacy behaviors from pre-Tokyo are not preserved.
    • ES5 Standards Mode: Default for global applications, facilitates ECMAScript 5 features such as "use strict", object property control, and modern Array/Date methods. It does not maintain legacy behaviors from pre-Helsinki.
    • Compatibility Mode: For older scripts, this mode supports legacy behaviors but lacks third-party library support. JSON methods are adapted to use the ES5 Native JSON object.

    Key Outcomes

    By configuring the appropriate JavaScript mode, you can ensure that your applications utilize the desired ECMAScript features. Transitioning between modes may alter existing script behaviors, so it is essential to review potential changes and test thoroughly when making adjustments.

    Utilizing ECMAScript 2021 (ES12) mode allows access to the latest JavaScript features, even within applications initially developed under older modes, enhancing functionality and performance.

    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.

    The JavaScript mode controls which JavaScript features you have access to in an application or script. The default mode for new scoped applications is ECMAScript 2021 (ES12) and for new global applications, it’s ES5 Standards. You can also turn on ECMAScript 2021 (ES12) mode for individual scripts in applications that use ES5 Standards or Compatibility mode.

    For more information about features supported by the ECMAScript 2021 (ES12) and ES5 Standards modes, see JavaScript engine feature support.

    ECMAScript 2021 (ES12) mode

    ECMAScript 2021 (ES12) mode is the default mode when you create new scoped applications. When you create new scripts, ECMAScript 2021 (ES12) mode is turned on by default regardless of the JavaScript mode configured for the application. This mode doesn’t preserve the legacy behaviors in the pre-Tokyo JavaScript engine or work with global scripts.

    ECMAScript 2021 (ES12) mode supports a subset of ECMAScript 2021 (ES12) and ECMAScript 2022 (ES13) syntax and features, including the following features:
    • Default function parameters
    • Rest parameters
    • For-of loops
    • Template literals
    • Destructuring
      • Declarations
      • Assignment
      • Parameters
    • Const declaration
    • Let declaration
    • Arrow functions
    • Class declarations
    • Map set
    • Optional chaining operator (?.)

    To learn about specific ECMAScript 2021 (ES12) features, see the Let's Learn ECMAScript 2021 videos on the ServiceNow Dev Program YouTube channel.

    ES5 Standards mode

    ES5 Standards mode is the default mode for global applications and is an option for scoped applications. This mode doesn’t preserve the legacy behaviors in the pre-Helsinki JavaScript engine.

    ES5 standards mode supports ECMAScript5 syntax and features, including the following features:
    • The "use strict" declaration
    • Control over extensibility of objects
    • Get and set properties on objects (accessors)
    • Control over writability, configurability, and enumerability of object properties
    • New Array and Date methods
    • Native JSON support
    • Support for modern third-party libraries such as lodash.js and moment.js

    Compatibility mode

    Compatibility mode is used for all scripts developed prior to the addition of ES5 Standards mode. Compatibility mode has some differences from the previous JavaScript engine.

    JSON support changes:
    • JSON.stringify() and JSON.parse() are implemented using the ES5 Native JSON object.
    • The new JSON().encode() and new JSON().decode() are still supported, but should only be used when the legacy behavior is required.

    The use of third-party JavaScript libraries isn’t supported in Compatibility mode.