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    @jridgewell/gen-mapping
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    0.3.2 • Public • Published

    @jridgewell/gen-mapping

    Generate source maps

    gen-mapping allows you to generate a source map during transpilation or minification. With a source map, you're able to trace the original location in the source file, either in Chrome's DevTools or using a library like @jridgewell/trace-mapping.

    You may already be familiar with the source-map package's SourceMapGenerator. This provides the same addMapping and setSourceContent API.

    Installation

    npm install @jridgewell/gen-mapping

    Usage

    import { GenMapping, addMapping, setSourceContent, toEncodedMap, toDecodedMap } from '@jridgewell/gen-mapping';
    
    const map = new GenMapping({
      file: 'output.js',
      sourceRoot: 'https://example.com/',
    });
    
    setSourceContent(map, 'input.js', `function foo() {}`);
    
    addMapping(map, {
      // Lines start at line 1, columns at column 0.
      generated: { line: 1, column: 0 },
      source: 'input.js',
      original: { line: 1, column: 0 },
    });
    
    addMapping(map, {
      generated: { line: 1, column: 9 },
      source: 'input.js',
      original: { line: 1, column: 9 },
      name: 'foo',
    });
    
    assert.deepEqual(toDecodedMap(map), {
      version: 3,
      file: 'output.js',
      names: ['foo'],
      sourceRoot: 'https://example.com/',
      sources: ['input.js'],
      sourcesContent: ['function foo() {}'],
      mappings: [
        [ [0, 0, 0, 0], [9, 0, 0, 9, 0] ]
      ],
    });
    
    assert.deepEqual(toEncodedMap(map), {
      version: 3,
      file: 'output.js',
      names: ['foo'],
      sourceRoot: 'https://example.com/',
      sources: ['input.js'],
      sourcesContent: ['function foo() {}'],
      mappings: 'AAAA,SAASA',
    });

    Smaller Sourcemaps

    Not everything needs to be added to a sourcemap, and needless markings can cause signficantly larger file sizes. gen-mapping exposes maybeAddSegment/maybeAddMapping APIs that will intelligently determine if this marking adds useful information. If not, the marking will be skipped.

    import { maybeAddMapping } from '@jridgewell/gen-mapping';
    
    const map = new GenMapping();
    
    // Adding a sourceless marking at the beginning of a line isn't useful.
    maybeAddMapping(map, {
      generated: { line: 1, column: 0 },
    });
    
    // Adding a new source marking is useful.
    maybeAddMapping(map, {
      generated: { line: 1, column: 0 },
      source: 'input.js',
      original: { line: 1, column: 0 },
    });
    
    // But adding another marking pointing to the exact same original location isn't, even if the
    // generated column changed.
    maybeAddMapping(map, {
      generated: { line: 1, column: 9 },
      source: 'input.js',
      original: { line: 1, column: 0 },
    });
    
    assert.deepEqual(toEncodedMap(map), {
      version: 3,
      names: [],
      sources: ['input.js'],
      sourcesContent: [null],
      mappings: 'AAAA',
    });

    Benchmarks

    node v18.0.0
    
    amp.js.map
    Memory Usage:
    gen-mapping: addSegment      5852872 bytes
    gen-mapping: addMapping      7716042 bytes
    source-map-js                6143250 bytes
    source-map-0.6.1             6124102 bytes
    source-map-0.8.0             6121173 bytes
    Smallest memory usage is gen-mapping: addSegment
    
    Adding speed:
    gen-mapping:      addSegment x 441 ops/sec ±2.07% (90 runs sampled)
    gen-mapping:      addMapping x 350 ops/sec ±2.40% (86 runs sampled)
    source-map-js:    addMapping x 169 ops/sec ±2.42% (80 runs sampled)
    source-map-0.6.1: addMapping x 167 ops/sec ±2.56% (80 runs sampled)
    source-map-0.8.0: addMapping x 168 ops/sec ±2.52% (80 runs sampled)
    Fastest is gen-mapping:      addSegment
    
    Generate speed:
    gen-mapping:      decoded output x 150,824,370 ops/sec ±0.07% (102 runs sampled)
    gen-mapping:      encoded output x 663 ops/sec ±0.22% (98 runs sampled)
    source-map-js:    encoded output x 197 ops/sec ±0.45% (84 runs sampled)
    source-map-0.6.1: encoded output x 198 ops/sec ±0.33% (85 runs sampled)
    source-map-0.8.0: encoded output x 197 ops/sec ±0.06% (93 runs sampled)
    Fastest is gen-mapping:      decoded output
    
    
    ***
    
    
    babel.min.js.map
    Memory Usage:
    gen-mapping: addSegment     37578063 bytes
    gen-mapping: addMapping     37212897 bytes
    source-map-js               47638527 bytes
    source-map-0.6.1            47690503 bytes
    source-map-0.8.0            47470188 bytes
    Smallest memory usage is gen-mapping: addMapping
    
    Adding speed:
    gen-mapping:      addSegment x 31.05 ops/sec ±8.31% (43 runs sampled)
    gen-mapping:      addMapping x 29.83 ops/sec ±7.36% (51 runs sampled)
    source-map-js:    addMapping x 20.73 ops/sec ±6.22% (38 runs sampled)
    source-map-0.6.1: addMapping x 20.03 ops/sec ±10.51% (38 runs sampled)
    source-map-0.8.0: addMapping x 19.30 ops/sec ±8.27% (37 runs sampled)
    Fastest is gen-mapping:      addSegment
    
    Generate speed:
    gen-mapping:      decoded output x 381,379,234 ops/sec ±0.29% (96 runs sampled)
    gen-mapping:      encoded output x 95.15 ops/sec ±2.98% (72 runs sampled)
    source-map-js:    encoded output x 15.20 ops/sec ±7.41% (33 runs sampled)
    source-map-0.6.1: encoded output x 16.36 ops/sec ±10.46% (31 runs sampled)
    source-map-0.8.0: encoded output x 16.06 ops/sec ±6.45% (31 runs sampled)
    Fastest is gen-mapping:      decoded output
    
    
    ***
    
    
    preact.js.map
    Memory Usage:
    gen-mapping: addSegment       416247 bytes
    gen-mapping: addMapping       419824 bytes
    source-map-js                1024619 bytes
    source-map-0.6.1             1146004 bytes
    source-map-0.8.0             1113250 bytes
    Smallest memory usage is gen-mapping: addSegment
    
    Adding speed:
    gen-mapping:      addSegment x 13,755 ops/sec ±0.15% (98 runs sampled)
    gen-mapping:      addMapping x 13,013 ops/sec ±0.11% (101 runs sampled)
    source-map-js:    addMapping x 4,564 ops/sec ±0.21% (98 runs sampled)
    source-map-0.6.1: addMapping x 4,562 ops/sec ±0.11% (99 runs sampled)
    source-map-0.8.0: addMapping x 4,593 ops/sec ±0.11% (100 runs sampled)
    Fastest is gen-mapping:      addSegment
    
    Generate speed:
    gen-mapping:      decoded output x 379,864,020 ops/sec ±0.23% (93 runs sampled)
    gen-mapping:      encoded output x 14,368 ops/sec ±4.07% (82 runs sampled)
    source-map-js:    encoded output x 5,261 ops/sec ±0.21% (99 runs sampled)
    source-map-0.6.1: encoded output x 5,124 ops/sec ±0.58% (99 runs sampled)
    source-map-0.8.0: encoded output x 5,434 ops/sec ±0.33% (96 runs sampled)
    Fastest is gen-mapping:      decoded output
    
    
    ***
    
    
    react.js.map
    Memory Usage:
    gen-mapping: addSegment       975096 bytes
    gen-mapping: addMapping      1102981 bytes
    source-map-js                2918836 bytes
    source-map-0.6.1             2885435 bytes
    source-map-0.8.0             2874336 bytes
    Smallest memory usage is gen-mapping: addSegment
    
    Adding speed:
    gen-mapping:      addSegment x 4,772 ops/sec ±0.15% (100 runs sampled)
    gen-mapping:      addMapping x 4,456 ops/sec ±0.13% (97 runs sampled)
    source-map-js:    addMapping x 1,618 ops/sec ±0.24% (97 runs sampled)
    source-map-0.6.1: addMapping x 1,622 ops/sec ±0.12% (99 runs sampled)
    source-map-0.8.0: addMapping x 1,631 ops/sec ±0.12% (100 runs sampled)
    Fastest is gen-mapping:      addSegment
    
    Generate speed:
    gen-mapping:      decoded output x 379,107,695 ops/sec ±0.07% (99 runs sampled)
    gen-mapping:      encoded output x 5,421 ops/sec ±1.60% (89 runs sampled)
    source-map-js:    encoded output x 2,113 ops/sec ±1.81% (98 runs sampled)
    source-map-0.6.1: encoded output x 2,126 ops/sec ±0.10% (100 runs sampled)
    source-map-0.8.0: encoded output x 2,176 ops/sec ±0.39% (98 runs sampled)
    Fastest is gen-mapping:      decoded output
    

    Keywords

    Install

    npm i @jridgewell/gen-mapping

    DownloadsWeekly Downloads

    21,928,810

    Version

    0.3.2

    License

    MIT

    Unpacked Size

    93 kB

    Total Files

    13

    Last publish

    Collaborators

    • jridgewell