Viewing github.com/facebook/react/scripts/rollup/stats.js

```
'use strict';
```
```
const Table = require('cli-table');
```
```
const filesize = require('filesize');
```
```
const chalk = require('chalk');
```
```
const join = require('path').join;
```
```
const fs = require('fs');
```
```
const mkdirp = require('mkdirp');
```

const BUNDLE_SIZES_FILE_NAME = join(__dirname, '../../build/bundle-sizes.json');

const prevBuildResults = fs.existsSync(BUNDLE_SIZES_FILE_NAME)

```
  ? require(BUNDLE_SIZES_FILE_NAME)
```
```
  : {bundleSizes: []};
```
```
const currentBuildResults = {
```

  // Mutated inside build.js during a build run.

```
  bundleSizes: [],
```
```
};
```
```
function saveResults() {
```
```
  if (process.env.CIRCLE_NODE_TOTAL) {
```

    // In CI, write the bundle sizes to a subdirectory and append the node index

    // to the filename. A downstream job will consolidate these into a

```
    // single file.
```

    const nodeIndex = process.env.CIRCLE_NODE_INDEX;

```
    mkdirp.sync('build/sizes');
```
```
    fs.writeFileSync(
```

      join('build', 'sizes', `bundle-sizes-${nodeIndex}.json`),

      JSON.stringify(currentBuildResults, null, 2)

```
    );
```
```
  } else {
```

    // Write all the bundle sizes to a single JSON file.

```
    fs.writeFileSync(
```
```
      BUNDLE_SIZES_FILE_NAME,
```

      JSON.stringify(currentBuildResults, null, 2)

```
    );
```
```
  }
```
```
}
```

function fractionalChange(prev, current) {

```
  return (current - prev) / prev;
```
```
}
```
```
function percentChangeString(change) {
```
```
  if (!isFinite(change)) {
```
```
    // When a new package is created
```
```
    return 'n/a';
```
```
  }
```

  const formatted = (change * 100).toFixed(1);

  if (/^-|^0(?:\.0+)$/.test(formatted)) {

```
    return `${formatted}%`;
```
```
  } else {
```
```
    return `+${formatted}%`;
```
```
  }
```
```
}
```
```
const resultsHeaders = [
```
```
  'Bundle',
```
```
  'Prev Size',
```
```
  'Current Size',
```
```
  'Diff',
```
```
  'Prev Gzip',
```
```
  'Current Gzip',
```
```
  'Diff',
```
```
];
```

function generateResultsArray(current, prevResults) {

```
  return current.bundleSizes
```
```
    .map(result => {
```

      const prev = prevResults.bundleSizes.filter(

```
        res =>
```

          res.filename === result.filename &&

          res.bundleType === result.bundleType

```
      )[0];
```
```
      if (result === prev) {
```

        // We didn't rebuild this bundle.

```
        return;
```
```
      }
```
```
      const size = result.size;
```
```
      const gzip = result.gzip;
```

      let prevSize = prev ? prev.size : 0;

      let prevGzip = prev ? prev.gzip : 0;

```
      return {
```
```
        filename: result.filename,
```
```
        bundleType: result.bundleType,
```

        packageName: result.packageName,

```
        prevSize: filesize(prevSize),
```
```
        prevFileSize: filesize(size),
```

        prevFileSizeChange: fractionalChange(prevSize, size),

        prevFileSizeAbsoluteChange: size - prevSize,

```
        prevGzip: filesize(prevGzip),
```
```
        prevGzipSize: filesize(gzip),
```

        prevGzipSizeChange: fractionalChange(prevGzip, gzip),

        prevGzipSizeAbsoluteChange: gzip - prevGzip,

```
      };
```
```
      // Strip any nulls
```
```
    })
```
```
    .filter(f => f);
```
```
}
```
```
function printResults() {
```
```
  const table = new Table({
```

    head: resultsHeaders.map(label => chalk.gray.yellow(label)),

```
  });
```

  const results = generateResultsArray(currentBuildResults, prevBuildResults);

```
  results.forEach(result => {
```
```
    table.push([
```

      chalk.white.bold(`${result.filename}  (${result.bundleType})`),

      chalk.gray.bold(result.prevSize),

      chalk.white.bold(result.prevFileSize),

      percentChangeString(result.prevFileSizeChange),

      chalk.gray.bold(result.prevGzip),

      chalk.white.bold(result.prevGzipSize),

      percentChangeString(result.prevGzipSizeChange),

```
    ]);
```
```
  });
```
```
  return table.toString();
```
```
}
```
```
module.exports = {
```
```
  currentBuildResults,
```
```
  generateResultsArray,
```
```
  printResults,
```
```
  saveResults,
```
```
  resultsHeaders,
```
```
};
```

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