85 lines
3.8 KiB
Markdown
85 lines
3.8 KiB
Markdown
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# babel-generator
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> Turns an AST into code.
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## Install
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```sh
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$ npm install babel-generator
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```
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## Usage
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```js
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import {parse} from 'babylon';
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import generate from 'babel-generator';
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const code = 'class Example {}';
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const ast = parse(code);
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const output = generate(ast, { /* options */ }, code);
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```
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## Options
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Options for formatting output:
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name | type | default | description
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-----------------------|----------|-----------------|--------------------------------------------------------------------------
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auxiliaryCommentBefore | string | | Optional string to add as a block comment at the start of the output file
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auxiliaryCommentAfter | string | | Optional string to add as a block comment at the end of the output file
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shouldPrintComment | function | `opts.comments` | Function that takes a comment (as a string) and returns `true` if the comment should be included in the output. By default, comments are included if `opts.comments` is `true` or if `opts.minifed` is `false` and the comment contains `@preserve` or `@license`
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retainLines | boolean | `false` | Attempt to use the same line numbers in the output code as in the source code (helps preserve stack traces)
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retainFunctionParens | boolean | `false` | Retain parens around function expressions (could be used to change engine parsing behavior)
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comments | boolean | `true` | Should comments be included in output
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compact | boolean or `'auto'` | `opts.minified` | Set to `true` to avoid adding whitespace for formatting
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minified | boolean | `false` | Should the output be minified
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concise | boolean | `false` | Set to `true` to reduce whitespace (but not as much as `opts.compact`)
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quotes | `'single'` or `'double'` | autodetect based on `ast.tokens` | The type of quote to use in the output
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filename | string | | Used in warning messages
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Options for source maps:
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name | type | default | description
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-----------------------|----------|-----------------|--------------------------------------------------------------------------
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sourceMaps | boolean | `false` | Enable generating source maps
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sourceMapTarget | string | | The filename of the generated code that the source map will be associated with
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sourceRoot | string | | A root for all relative URLs in the source map
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sourceFileName | string | | The filename for the source code (i.e. the code in the `code` argument). This will only be used if `code` is a string.
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## AST from Multiple Sources
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In most cases, Babel does a 1:1 transformation of input-file to output-file. However,
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you may be dealing with AST constructed from multiple sources - JS files, templates, etc.
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If this is the case, and you want the sourcemaps to reflect the correct sources, you'll need
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to make some changes to your code.
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First, each node with a `loc` property (which indicates that node's original placement in the
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source document) must also include a `loc.filename` property, set to the source filename.
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Second, you should pass an object to `generate` as the `code` parameter. Keys
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should be the source filenames, and values should be the source content.
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Here's an example of what that might look like:
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```js
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import {parse} from 'babylon';
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import generate from 'babel-generator';
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const a = 'var a = 1;';
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const b = 'var b = 2;';
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const astA = parse(a, { filename: 'a.js' });
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const astB = parse(b, { filename: 'b.js' });
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const ast = {
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type: 'Program',
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body: [].concat(astA.body, ast2.body)
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};
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const { code, map } = generate(ast, { /* options */ }, {
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'a.js': a,
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'b.js': b
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});
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// Sourcemap will point to both a.js and b.js where appropriate.
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```
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