Viewing github.com/facebook/react/scripts/error-codes/extract-errors.js

```
'use strict';
```
```
const fs = require('fs');
```
```
const path = require('path');
```

const {execSync} = require('child_process');

```
async function main() {
```
```
  const originalJSON = JSON.parse(
```

    fs.readFileSync(path.resolve(__dirname, '../error-codes/codes.json'))

```
  );
```
```
  const existingMessages = new Set();
```

  const codes = Object.keys(originalJSON);

```
  let nextCode = 0;
```

  for (let i = 0; i < codes.length; i++) {

```
    const codeStr = codes[i];
```

    const message = originalJSON[codeStr];

    const code = parseInt(codeStr, 10);

```
    existingMessages.add(message);
```
```
    if (code >= nextCode) {
```
```
      nextCode = code + 1;
```
```
    }
```
```
  }
```

  console.log('Searching `build` directory for unminified errors...\n');

```
  let out;
```
```
  try {
```
```
    out = execSync(
```

      "git --no-pager grep -n --untracked --no-exclude-standard '/*! <expected-error-format>' -- build"

```
    ).toString();
```
```
  } catch (e) {
```

    if (e.status === 1 && e.stdout.toString() === '') {

```
      // No unminified errors found.
```
```
      return;
```
```
    }
```
```
    throw e;
```
```
  }
```
```
  let newJSON = null;
```

  const regex = /\<expected-error-format\>"(.+?)"\<\/expected-error-format\>/g;

```
  do {
```
```
    const match = regex.exec(out);
```
```
    if (match === null) {
```
```
      break;
```
```
    } else {
```
```
      const message = match[1].trim();
```

      if (existingMessages.has(message)) {

        // This probably means you ran the script twice.

```
        continue;
```
```
      }
```
```
      existingMessages.add(message);
```
```
      // Add to json map
```
```
      if (newJSON === null) {
```

        newJSON = Object.assign({}, originalJSON);

```
      }
```

      console.log(`"${nextCode}": "${message}"`);

```
      newJSON[nextCode] = message;
```
```
      nextCode += 1;
```
```
    }
```
```
  } while (true);
```
```
  if (newJSON) {
```
```
    fs.writeFileSync(
```

      path.resolve(__dirname, '../error-codes/codes.json'),

```
      JSON.stringify(newJSON, null, 2)
```
```
    );
```
```
  }
```
```
}
```
```
main().catch(error => {
```
```
  console.error(error);
```
```
  process.exit(1);
```
```
});
```

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