Write Mapbox GL expressions in a more familiar, handwritable, spreadsheet-like, programming-like syntax.
npm install @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.
- Most expressions are represented like function invocations in programming, e.g. get("population"), log2(get("population")).
- Symbolic math operators (+ - / %) and parentheses work like in high school math, e.g. ((3 + 4) 2) / 7.
That is, the formula should contain 3 + 4 instead of +(3, 4).
- Symbolic decision operators also work with operands on both sides, instead of like function invocations.
So get("foo") != 4 instead of !=(get("foo"), 4).
- Strings must always be wrapped in quotation marks, e.g. concat("egg", "s") not concat(egg, s).
- & operator concatenates strings, as in spreadsheet programs.
``js
// Input
2 + 2
// Output
["+", 2, 2]
`
`js
// Input
max(3, log2(6))
// Output
["max", 3, ["log2", 6]]
`
`js
// Input
((3 + get("num")) * 2) / 7
// Output
["/", ["*", ["+", 3, get("num")], 2], 7]
`
`js
// Input
"name: " & get("name")
// Output
["concat", ["name ", ["get", "name"]]]
`
The module exports two functions so you can transform in both directions:
- formulaToExpression transforms (string) formulas to (array) expressions.expressionToFormula
- transforms expressions to formulas.
`js
import jamsession from '@mapbox/expression-jamsession';
jamsession.formulaToExpression("3 + 4"); // ["+", 3, 4]
jamsession.expressionToFormula(["+", 3, 4]); // "3 + 4"
`
This library should work in IE11+. It uses a Set, so you might get it working in older browsers by adding a polyfill.
- You can use this library to create expressions that are syntactically acceptable but invalid as Mapbox GL expressions, e.g. get(true) outputs ["get", true], which fails.literal` expression.
- You cannot use JSON object literal arguments to the
This is allowed in the spec; but objects are not supported by jsep and the use case for this type of expression is kind of an edge case — so it's probably not worth trying to adjust the parser to support this edge case.
If you disagree, please consider filing an issue and/or PR.