@mapbox/expression-jamsession

@mapbox/expression-jamsession

Write Mapbox GL expressions in a more familiar, handwritable, spreadsheet-like, programming-like syntax. This library translates these handwritten formulas into valid spec-compliant Mapbox GL expressions that you can use in a Mapbox style.

Formula syntax features

• Arithmetic operators (+ - * /) and parentheses work like in high school math, e.g. ((3 + 4) * 2) / 7.
• Expressions are represented like function invocations in programming, e.g. get("population"), log2(get("population")).
• & operator concatenates strings, as in spreadsheet programs.

// Input
2 + 2

// Output
["+", 2, 2]

// Input
max(3, log2(6))

// Output
["max", 3, ["log2", 6]]

// Input
((3 + get("num")) * 2) / 7

// Output
["/", ["*", ["+", 3, get("num")], 2], 7]

// Input
"name: " & get("name")

// Output
["concat", ["name ", ["get", "name"]]]

Usage

The module exports two functions so you can transform in both directions:

• formulaToExpression transforms (string) formulas to (array) expressions.
• expressionToFormula transforms expressions to formulas.

import jamsession from '@mapbox/expression-jamsession';

jamsession.formulaToExpression("3 + 4"); // ["+", 3, 4]

jamsession.expressionToFormula(["+", 3, 4]); // "3 + 4"

Caveats

• You can use this library to create expressions that are syntactically acceptable but invalid as Mapbox GL expressions, e.g. notARealExpression(true) outputs ["notARealExpression", true].

Changelog

0.3.0

• Fix handling of ^ (exponentiation) and % (remainder) expression operators.
• Fix handling of empty input to formulaToExpression. It now returns undefined.
• Fix handling of hyphenated expression operators.