fastLowess WebAssembly API Reference

The WebAssembly bindings provide a high-performance interface to the core Rust library, mirroring the Rust API structure.

Classes and Functions

smooth

The smooth function is the main entry point for batch smoothing.

Signature:

const result = smooth(x, y, options);

• x: Float64Array of input x values.
• y: Float64Array of input y values.
• options: An object containing LowessOptions fields.
• Returns: A LowessResult object.

StreamingLowessWasm

The StreamingLowessWasm class processes data in chunks, suitable for very large datasets or streaming applications.

Constructor:

const stream = new StreamingLowessWasm(options, streamingOptions);

• options: An object containing LowessOptions fields.
• streamingOptions: An object containing StreamingOptions fields.

Methods:

const partialResult = stream.processChunk(x, y);

• Processes a chunk of data. Returns partial results.

const finalResult = stream.finalize();

• Finalizes the smoothing process and returns any remaining buffered results.

OnlineLowessWasm

The OnlineLowessWasm class updates the model incrementally with new data points.

Constructor:

const online = new OnlineLowessWasm(options, onlineOptions);

• options: An object containing LowessOptions fields.
• onlineOptions: An object containing OnlineOptions fields.

Methods:

const result = online.update(x, y);

• Adds new points to the model and returns the smoothed values (retrospective or prospective depending on mode).

Options Structures

LowessOptions

Field	Type	Default	Description
fraction	number	0.67	Smoothing fraction (bandwidth)
iterations	number	3	Number of robustifying iterations
delta	number	NaN	Interpolation distance (NaN for auto)
weightFunction	string	"tricube"	Weight function name
robustnessMethod	string	"bisquare"	Robustness method name
scalingMethod	string	"mad"	Residual scaling method
boundaryPolicy	string	"extend"	Boundary handling policy
zeroWeightFallback	string	"useLocalMean"	Zero-weight handling strategy
autoConverge	number	null	Auto-convergence tolerance
confidenceIntervals	number	null	Confidence level (e.g., 0.95)
predictionIntervals	number	null	Prediction level (e.g., 0.95)
returnDiagnostics	boolean	false	Include diagnostics in result
returnResiduals	boolean	false	Include residuals in result
returnRobustnessWeights	boolean	false	Include weights in result
cvMethod	string	"kfold"	Cross-validation method ("kfold")
cvK	number	5	Number of CV folds
cvFractions	number[]	null	Manual fractions for CV grid

StreamingOptions

Field	Type	Default	Description
chunkSize	number	5000	Data chunk size
overlap	number	500	Overlap size (-1 for auto)
mergeStrategy	string	"average"	Merge strategy for overlap

OnlineOptions

Field	Type	Default	Description
windowCapacity	number	100	Max window size
minPoints	number	2	Min points before smoothing
updateMode	string	"incremental"	Update mode ("full" or "incremental")

Result Structure

LowessResult

Field	Type	Description
x	Float64Array	Smoothed X coordinates
y	Float64Array	Smoothed Y coordinates
valid	boolean	True if result is valid
error	string	Error message if failed
diagnostics	Diagnostics	Diagnostic metrics object
residuals	Float64Array	Residuals (if requested)
confidenceLower	Float64Array	Lower CI bounds
confidenceUpper	Float64Array	Upper CI bounds
predictionLower	Float64Array	Lower PI bounds
predictionUpper	Float64Array	Upper PI bounds
robustnessWeights	Float64Array	Robustness weights

Diagnostics

Field	Type	Description
rmse	number	Root Mean Squared Error
mae	number	Mean Absolute Error
rSquared	number	R-squared
residualSd	number	Residual standard deviation
effectiveDf	number	Effective degrees of freedom
aic	number	AIC
aicc	number	AICc

String Options

Weight Functions

• "tricube" (default)
• "epanechnikov"
• "gaussian"
• "uniform"
• "biweight"
• "triangle"
• "cosine"

Robustness Methods

• "bisquare" (default)
• "huber"
• "talwar"

Boundary Policies

• "extend" (default - linear extrapolation)
• "reflect"
• "zero"
• "noBoundary"

Scaling Methods

• "mad" (default - Median Absolute Deviation)
• "mar" (Median Absolute Residual)
• "mean" (Mean Absolute Residual)

Zero Weight Fallback

• "useLocalMean" (default)
• "returnOriginal"
• "returnNone"

Merge Strategies (Streaming)

• "weighted" (default - weighted average of overlapping chunks)
• "average"
• "left"
• "right"

Update Modes (Online)

• "full" (default - re-smooth entire window)
• "incremental" (O(1) update using existing fit)

Example

import init, { smooth } from 'fastlowess-wasm';

await init();

const x = new Float64Array([1, 2, 3, 4, 5]);
const y = new Float64Array([2.1, 4.0, 6.2, 8.0, 10.1]);

// Fit data
const result = smooth(x, y, { fraction: 0.5 });

console.log("Smoothed Y:", result.y);