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Created Exports Files (markdown)

elemoine
2012-10-29 16:56:57 -07:00
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Exports-Files.md
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Alongside js files the src dir includes "exports files" (e.g. src/ol/map.exports). An export file declares symbols and properties that are to be exported when creating builds of the library. For example the src/ol/map.exports file includes this:
```
@exportClass ol.Map ol.MapOptions
@exportProperty ol.Map.prototype.getControls
```
This declares that the `ol.Map` symbol, and that the `ol.Map.prototype.getControls` property, should be exported, i.e. made available to lib users.
Exports files are processed by the `bin/generate-exports` script, using its `--exports` switch. This script receives a list of exports files as its input, and outputs `@exportSymbol` and `@exportProperty` statements. The `Makefile` places the output of the `generate-exports --exports` command in the `build/src/external/src/exports.js` file. This js file is then used as an input file for the `ol.js` build (see `build/ol.json`).
Note: the `src/google.exports` file just makes the `goog.require` function be exported as a null function. This is just to be able to execute the examples both in dev mode (mode=RAW) – where `goog.require` statements are required – and with the `ol.js` build.
The `src/objectlitterals.exports` file is specific. This file declares the config objects and properties for single-arg constructors. These declarations are done with the `@exportObjectLitteral` and `@exportObjectLitteralProperty` directives. This file is also processed with the `bin/generate-exports` script, but using the `--externs` and `--typedef` switches. The `generate-exports --externs` generates Closure externs from the `@exportObjectLitteral` and `@exportObjectLitteralProperty` directives. The Makefile places these externs in the `build/src/external/externs/types.js` file, which is used as a regular externs file by the Closure compiler (see `build/ol.json`). The `generate-exports --typedef` command generate typedef's for the object litterals declared with @exportObjectLitteral and `@exportObjectLitteralProperty`. The `Makefile` places the typedef's in the `build/src/external/src/types.js`, which, like `exports.js`, is used as an input file for the ol.js build (see `build/ol.json`). Externs define types for config objects created by lib users, while typedef's define types created internally by the lib.
OL3 devs need to create new exports files when adding new API elements to the lib. They also need to declare single-arg constructors' config objects and properties in `src/objectlitterals.exports`.