51Degrees JavaScript builder

The JavaScript builder element renders a client-side JavaScript include from the JSON payload produced by the [fiftyone_json_builder] crate. The generated script creates a global manager object on the client device, runs any JavaScript-typed properties the JSON carries, and (when a callback URL is configured) posts the evidence it gathers back to the server for a refreshed result. It implements the javascript-builder specification.

The template

The script is rendered from a single Mustache template, JavaScriptResource.mustache, embedded at compile time with include_str!. Rendering uses a small, pure-safe-Rust Mustache renderer (in this crate's mustache module) with HTML escaping disabled, so the JSON payload, the callback URL and the object name reach the client verbatim.

Configuration and per-request overrides

[JavaScriptBuilderElementBuilder] sets the host, endpoint, protocol, object name, cookie behavior and minification. Several of those can be overridden per request through evidence (query.fod-js-object-name, query.fod-js-enable-cookies, header.host and header.protocol). See [JavaScriptBuilderElement] for the full derivation rules.

Minification

With the default-on minify feature the rendered script is minified by the oxc toolchain (see the minify module). A minification failure falls back to the unminified script, so valid JavaScript is always served. The set_minify builder flag turns minification off for an element, and building the crate with default-features = false drops the oxc dependency entirely.

A worked pipeline

use std::sync::Arc;
use fiftyone_pipeline_core::{Evidence, Pipeline};
use fiftyone_json_builder::JsonBuilderElement;
use fiftyone_javascript_builder::{JavaScriptBuilderElement, JAVASCRIPT_BUILDER_DATA_KEY};

let pipeline = Pipeline::builder()
    .add_element(Arc::new(JsonBuilderElement::new()))
    .add_element(Arc::new(JavaScriptBuilderElement::new()))
    .build()
    .unwrap();

let mut data = pipeline.create_flow_data_with(
    Evidence::builder().add("header.host", "localhost").build(),
);
data.process().unwrap();

let js = data.get(JAVASCRIPT_BUILDER_DATA_KEY).unwrap().javascript().to_owned();
assert!(js.contains("fiftyoneDegreesManager"));