vega2ol

library1.1.1jsnpmunverified

A TypeScript library that transpiles Vega expressions to OpenLayers array-based expression format. v1.1.1 (latest), stable release. Key differentiator: bridges Vega-Lite/Vega visualization specs with OpenLayers map styling by converting conditional logic, math/string/array functions, and member access (e.g., datum.field) into OpenLayers expressions like ['case', ['>', ['get', 'value'], 100], 'red', 'blue']. Ideal for OpenLayers users who prefer Vega's concise JavaScript-like syntax.

serialization

npm install vega2ol

github ↗package ↗

INSTALL

IMPORT

SIG · VEGA2OL

vega2ol

serializationjavascriptv1.1.1

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

vega2ol

✓ import { vega2ol } from 'vega2ol'

✗ const vega2ol = require('vega2ol')

ESM-only, shipped with TypeScript type definitions. Named export only; no default export.

vega2ol (default import)

✓ import { vega2ol } from 'vega2ol'

✗ import vega2ol from 'vega2ol'

Only a named export exists. Default import is not valid and will throw at runtime.

VegaToOLVisitor

✓ import { VegaToOLVisitor } from 'vega2ol'

✗ import { Visitor } from 'vega2ol'

Class for advanced usage if you need to extend or customize the transpiler. Exported but typically not imported directly; use vega2ol() function instead.

Transpile a Vega conditional expression to OpenLayers format and apply to a style object.

import { vega2ol } from 'vega2ol'; const vegaExpr = "datum.population > 1000000 ? '#FF0000' : '#0000FF'"; const olExpr = vega2ol(vegaExpr); console.log(olExpr); // ['case', ['>', ['get', 'population'], 1000000], '#FF0000', '#0000FF'] const style = { 'fill-color': olExpr, 'fill-opacity': vega2ol("datum.category == 'important' ? 1 : 0.5") }; console.log(style);

Debug

Known issues

gotchavega2ol does not support all Vega functions (e.g., instanceof, regexp). Unsupported functions will cause a runtime error.

fix

Check the documentation for a list of supported functions. Use only supported functionality or manually translate complex expressions.

affects: <=1.1.1

gotchaThe library uses vega-expression to parse expressions, which may have its own quirks (e.g., strict syntax). Incorrect Vega syntax will throw parse errors.

fix

Ensure your Vega expression is valid per Vega specification; avoid trailing commas or invalid operators.

affects: >=1.0.0

gotchaOpenLayers expression format is array-based, not an object or string. vega2ol returns arrays; do not stringify them prematurely.

fix

Use the returned array directly in OpenLayers style objects; do not call JSON.stringify() unless you intend to send it as data.

affects: >=1.0.0

gotchaMember access like datum.x is always converted to ['get', 'x'], which reads from OpenLayers feature properties. If your data is stored differently (e.g., in a different property name), you need to adjust the expression.

fix

Use only datum.fieldName pattern; OpenLayers expressions use ['get', 'x'] to access feature attributes. Ensure your feature has the expected property keys.

affects: >=1.0.0

Errors

Common errors & fixes

TypeError: Cannot find module 'vega2ol'

Missing installation or incorrect import in CommonJS environment.

fix

Ensure the package is installed: npm install vega2ol. Use ESM import syntax: import { vega2ol } from 'vega2ol'.

Error: Unsupported expression type: CallExpression with function 'myFunc'

The expression uses a function not supported by vega2ol.

fix

Use only supported functions: floor, ceil, round, abs, sqrt, pow, log, exp, sin, cos, tan, min, max, tostring, upper, lower, substring, length, indexof, slice, type, isvalid, isnumber, isstring, isboolean.

SyntaxError: Expected ')' but got ';'

Vega expression syntax error, often due to trailing semicolon or extra punctuation.

fix

Remove trailing semicolons and ensure valid Vega expression syntax. For example, use datum.x > 5 ? 'a' : 'b' without semicolons.

TypeError: vega2ol is not a function

Using default import instead of named import.

fix

Change import statement to import { vega2ol } from 'vega2ol'.

Upgrade

Version history

1.1.1latest on npm

Audit

Dependencies

vega-expressionrequiredParses Vega expression strings into an Abstract Syntax Tree (AST) for transpilation.

Agent activity

7 hits · last 30 days

node

OpenAI (training)

Resources

githubhttps://github.com/geojupyter/vega2ol ↗

packagehttps://www.npmjs.com/package/vega2ol ↗