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# sourcemap-codec
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Encode/decode the `mappings` property of a [sourcemap](https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit).
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## Why?
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Sourcemaps are difficult to generate and manipulate, because the `mappings` property – the part that actually links the generated code back to the original source – is encoded using an obscure method called [Variable-length quantity](https://en.wikipedia.org/wiki/Variable-length_quantity). On top of that, each segment in the mapping contains offsets rather than absolute indices, which means that you can't look at a segment in isolation – you have to understand the whole sourcemap.
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This package makes the process slightly easier.
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## Installation
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```bash
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npm install sourcemap-codec
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```
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## Usage
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```js
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import { encode, decode } from 'sourcemap-codec';
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var decoded = decode( ';EAEEA,EAAE,EAAC,CAAE;ECQY,UACC' );
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assert.deepEqual( decoded, [
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// the first line (of the generated code) has no mappings,
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// as shown by the starting semi-colon (which separates lines)
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[],
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// the second line contains four (comma-separated) segments
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[
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// segments are encoded as you'd expect:
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// [ generatedCodeColumn, sourceIndex, sourceCodeLine, sourceCodeColumn, nameIndex ]
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// i.e. the first segment begins at column 2, and maps back to the second column
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// of the second line (both zero-based) of the 0th source, and uses the 0th
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// name in the `map.names` array
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[ 2, 0, 2, 2, 0 ],
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// the remaining segments are 4-length rather than 5-length,
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// because they don't map a name
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[ 4, 0, 2, 4 ],
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[ 6, 0, 2, 5 ],
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[ 7, 0, 2, 7 ]
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],
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// the final line contains two segments
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[
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[ 2, 1, 10, 19 ],
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[ 12, 1, 11, 20 ]
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]
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]);
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var encoded = encode( decoded );
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assert.equal( encoded, ';EAEEA,EAAE,EAAC,CAAE;ECQY,UACC' );
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```
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# License
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MIT
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