expression-jamsession
所属分类：智慧办公
开发工具：JavaScript
文件大小：77KB
下载次数：0
上传日期：2021-09-24 18:46:19
上 传 者：
sh-1993
说明： 以更熟悉的、可手写的、类似电子表格的、类似编程的语法编写Mapbox GL表达式。
(Write Mapbox GL expressions in a more familiar, handwritable, spreadsheet- like, programming-like syntax.)
文件列表:
.eslintignore (5, 2021-09-25)
.eslintrc.json (211, 2021-09-25)
.travis.yml (115, 2021-09-25)
CHANGELOG.md (1394, 2021-09-25)
CODEOWNERS (108, 2021-09-25)
CODE_OF_CONDUCT.md (1932, 2021-09-25)
LICENSE (1263, 2021-09-25)
package-lock.json (301367, 2021-09-25)
package.json (1938, 2021-09-25)
rollup.config.js (375, 2021-09-25)
scripts (0, 2021-09-25)
scripts\.eslintrc.json (359, 2021-09-25)
scripts\build-operator-list.js (580, 2021-09-25)
src (0, 2021-09-25)
src\expression-operators.js (2253, 2021-09-25)
src\expression-to-formula.js (1947, 2021-09-25)
src\formula-to-expression.js (3649, 2021-09-25)
src\handle-syntax-errors.js (653, 2021-09-25)
src\index.js (184, 2021-09-25)
test (0, 2021-09-25)
test\.eslintrc.json (36, 2021-09-25)
test\expression-to-formula.test.js (6001, 2021-09-25)
test\formula-to-expression.test.js (10150, 2021-09-25)
# @mapbox/expression-jamsession
[](https://travis-ci.com/mapbox/expression-jamsession)
Write [Mapbox GL expressions](https://www.mapbox.com/mapbox-gl-js/style-spec/#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
- 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"]]]
```
## 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.
```js
import jamsession from '@mapbox/expression-jamsession';
jamsession.formulaToExpression("3 + 4"); // ["+", 3, 4]
jamsession.expressionToFormula(["+", 3, 4]); // "3 + 4"
```
## Browser compatibility
This library should work in IE11+. It uses a `Set`, so you might get it working in older browsers by adding a polyfill.
## Caveats
- 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.
- You cannot use JSON object literal arguments to [the `literal` expression](https://www.mapbox.com/mapbox-gl-js/style-spec/#expressions-types-literal).
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.
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