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228 lines
7.3 KiB
228 lines
7.3 KiB
4 weeks ago
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# @jridgewell/gen-mapping
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> Generate source maps
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`gen-mapping` allows you to generate a source map during transpilation or minification.
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With a source map, you're able to trace the original location in the source file, either in Chrome's
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DevTools or using a library like [`@jridgewell/trace-mapping`][trace-mapping].
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You may already be familiar with the [`source-map`][source-map] package's `SourceMapGenerator`. This
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provides the same `addMapping` and `setSourceContent` API.
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## Installation
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```sh
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npm install @jridgewell/gen-mapping
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```
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## Usage
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```typescript
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import { GenMapping, addMapping, setSourceContent, toEncodedMap, toDecodedMap } from '@jridgewell/gen-mapping';
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const map = new GenMapping({
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file: 'output.js',
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sourceRoot: 'https://example.com/',
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});
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setSourceContent(map, 'input.js', `function foo() {}`);
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addMapping(map, {
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// Lines start at line 1, columns at column 0.
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generated: { line: 1, column: 0 },
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source: 'input.js',
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original: { line: 1, column: 0 },
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});
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addMapping(map, {
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generated: { line: 1, column: 9 },
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source: 'input.js',
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original: { line: 1, column: 9 },
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name: 'foo',
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});
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assert.deepEqual(toDecodedMap(map), {
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version: 3,
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file: 'output.js',
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names: ['foo'],
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sourceRoot: 'https://example.com/',
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sources: ['input.js'],
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sourcesContent: ['function foo() {}'],
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mappings: [
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[ [0, 0, 0, 0], [9, 0, 0, 9, 0] ]
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],
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});
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assert.deepEqual(toEncodedMap(map), {
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version: 3,
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file: 'output.js',
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names: ['foo'],
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sourceRoot: 'https://example.com/',
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sources: ['input.js'],
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sourcesContent: ['function foo() {}'],
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mappings: 'AAAA,SAASA',
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});
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```
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### Smaller Sourcemaps
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Not everything needs to be added to a sourcemap, and needless markings can cause signficantly
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larger file sizes. `gen-mapping` exposes `maybeAddSegment`/`maybeAddMapping` APIs that will
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intelligently determine if this marking adds useful information. If not, the marking will be
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skipped.
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```typescript
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import { maybeAddMapping } from '@jridgewell/gen-mapping';
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const map = new GenMapping();
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// Adding a sourceless marking at the beginning of a line isn't useful.
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maybeAddMapping(map, {
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generated: { line: 1, column: 0 },
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});
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// Adding a new source marking is useful.
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maybeAddMapping(map, {
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generated: { line: 1, column: 0 },
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source: 'input.js',
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original: { line: 1, column: 0 },
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});
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// But adding another marking pointing to the exact same original location isn't, even if the
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// generated column changed.
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maybeAddMapping(map, {
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generated: { line: 1, column: 9 },
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source: 'input.js',
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original: { line: 1, column: 0 },
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});
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assert.deepEqual(toEncodedMap(map), {
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version: 3,
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names: [],
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sources: ['input.js'],
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sourcesContent: [null],
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mappings: 'AAAA',
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});
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```
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## Benchmarks
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```
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node v18.0.0
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amp.js.map
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Memory Usage:
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gen-mapping: addSegment 5852872 bytes
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gen-mapping: addMapping 7716042 bytes
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source-map-js 6143250 bytes
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source-map-0.6.1 6124102 bytes
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source-map-0.8.0 6121173 bytes
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Smallest memory usage is gen-mapping: addSegment
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Adding speed:
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gen-mapping: addSegment x 441 ops/sec ±2.07% (90 runs sampled)
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gen-mapping: addMapping x 350 ops/sec ±2.40% (86 runs sampled)
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source-map-js: addMapping x 169 ops/sec ±2.42% (80 runs sampled)
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source-map-0.6.1: addMapping x 167 ops/sec ±2.56% (80 runs sampled)
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source-map-0.8.0: addMapping x 168 ops/sec ±2.52% (80 runs sampled)
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Fastest is gen-mapping: addSegment
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Generate speed:
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gen-mapping: decoded output x 150,824,370 ops/sec ±0.07% (102 runs sampled)
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gen-mapping: encoded output x 663 ops/sec ±0.22% (98 runs sampled)
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source-map-js: encoded output x 197 ops/sec ±0.45% (84 runs sampled)
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source-map-0.6.1: encoded output x 198 ops/sec ±0.33% (85 runs sampled)
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source-map-0.8.0: encoded output x 197 ops/sec ±0.06% (93 runs sampled)
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Fastest is gen-mapping: decoded output
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***
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babel.min.js.map
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Memory Usage:
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gen-mapping: addSegment 37578063 bytes
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gen-mapping: addMapping 37212897 bytes
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source-map-js 47638527 bytes
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source-map-0.6.1 47690503 bytes
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source-map-0.8.0 47470188 bytes
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Smallest memory usage is gen-mapping: addMapping
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Adding speed:
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gen-mapping: addSegment x 31.05 ops/sec ±8.31% (43 runs sampled)
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gen-mapping: addMapping x 29.83 ops/sec ±7.36% (51 runs sampled)
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source-map-js: addMapping x 20.73 ops/sec ±6.22% (38 runs sampled)
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source-map-0.6.1: addMapping x 20.03 ops/sec ±10.51% (38 runs sampled)
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source-map-0.8.0: addMapping x 19.30 ops/sec ±8.27% (37 runs sampled)
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Fastest is gen-mapping: addSegment
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Generate speed:
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gen-mapping: decoded output x 381,379,234 ops/sec ±0.29% (96 runs sampled)
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gen-mapping: encoded output x 95.15 ops/sec ±2.98% (72 runs sampled)
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source-map-js: encoded output x 15.20 ops/sec ±7.41% (33 runs sampled)
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source-map-0.6.1: encoded output x 16.36 ops/sec ±10.46% (31 runs sampled)
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source-map-0.8.0: encoded output x 16.06 ops/sec ±6.45% (31 runs sampled)
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Fastest is gen-mapping: decoded output
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***
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preact.js.map
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Memory Usage:
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gen-mapping: addSegment 416247 bytes
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gen-mapping: addMapping 419824 bytes
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source-map-js 1024619 bytes
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source-map-0.6.1 1146004 bytes
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source-map-0.8.0 1113250 bytes
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Smallest memory usage is gen-mapping: addSegment
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Adding speed:
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gen-mapping: addSegment x 13,755 ops/sec ±0.15% (98 runs sampled)
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gen-mapping: addMapping x 13,013 ops/sec ±0.11% (101 runs sampled)
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source-map-js: addMapping x 4,564 ops/sec ±0.21% (98 runs sampled)
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source-map-0.6.1: addMapping x 4,562 ops/sec ±0.11% (99 runs sampled)
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source-map-0.8.0: addMapping x 4,593 ops/sec ±0.11% (100 runs sampled)
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Fastest is gen-mapping: addSegment
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Generate speed:
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gen-mapping: decoded output x 379,864,020 ops/sec ±0.23% (93 runs sampled)
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gen-mapping: encoded output x 14,368 ops/sec ±4.07% (82 runs sampled)
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source-map-js: encoded output x 5,261 ops/sec ±0.21% (99 runs sampled)
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source-map-0.6.1: encoded output x 5,124 ops/sec ±0.58% (99 runs sampled)
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source-map-0.8.0: encoded output x 5,434 ops/sec ±0.33% (96 runs sampled)
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Fastest is gen-mapping: decoded output
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***
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react.js.map
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Memory Usage:
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gen-mapping: addSegment 975096 bytes
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gen-mapping: addMapping 1102981 bytes
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source-map-js 2918836 bytes
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source-map-0.6.1 2885435 bytes
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source-map-0.8.0 2874336 bytes
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Smallest memory usage is gen-mapping: addSegment
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Adding speed:
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gen-mapping: addSegment x 4,772 ops/sec ±0.15% (100 runs sampled)
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gen-mapping: addMapping x 4,456 ops/sec ±0.13% (97 runs sampled)
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source-map-js: addMapping x 1,618 ops/sec ±0.24% (97 runs sampled)
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source-map-0.6.1: addMapping x 1,622 ops/sec ±0.12% (99 runs sampled)
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source-map-0.8.0: addMapping x 1,631 ops/sec ±0.12% (100 runs sampled)
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Fastest is gen-mapping: addSegment
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Generate speed:
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gen-mapping: decoded output x 379,107,695 ops/sec ±0.07% (99 runs sampled)
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gen-mapping: encoded output x 5,421 ops/sec ±1.60% (89 runs sampled)
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source-map-js: encoded output x 2,113 ops/sec ±1.81% (98 runs sampled)
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source-map-0.6.1: encoded output x 2,126 ops/sec ±0.10% (100 runs sampled)
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source-map-0.8.0: encoded output x 2,176 ops/sec ±0.39% (98 runs sampled)
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Fastest is gen-mapping: decoded output
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```
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[source-map]: https://www.npmjs.com/package/source-map
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[trace-mapping]: https://github.com/jridgewell/trace-mapping
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