parcel/packages/packagers/js/src/ESMOutputFormat.js at efc3575438e509450a050cfb11c46831c04c91c5 · parcel-bundler/parcel · GitHub

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// @flow
import type {
  ScopeHoistingPackager,
  OutputFormat,
} from './ScopeHoistingPackager';

export class ESMOutputFormat implements OutputFormat {
  packager: ScopeHoistingPackager;

  constructor(packager: ScopeHoistingPackager) {
    this.packager = packager;
  }

  buildBundlePrelude(): [string, number] {
    let res = '';
    let lines = 0;
    for (let [source, specifiers] of this.packager.externals) {
      let defaultSpecifier = null;
      let namespaceSpecifier = null;
      let namedSpecifiers = [];
      for (let [imported, symbol] of specifiers) {
        if (imported === 'default' /* || isCommonJS*/) {
          defaultSpecifier = symbol;
        } else if (imported === '*') {
          namespaceSpecifier = `* as ${symbol}`;
        } else {
          let specifier = imported;
          if (symbol !== imported) {
            specifier += ` as ${symbol}`;
          }

          namedSpecifiers.push(specifier);
        }
      }

      // ESModule syntax allows combining default and namespace specifiers, or default and named, but not all three.

      let imported = '';
      if (namespaceSpecifier) {
        let s = namespaceSpecifier;
        if (defaultSpecifier) {
          s = `${defaultSpecifier}, ${namespaceSpecifier}`;
        }

        res += `import ${s} from ${JSON.stringify(source)};\n`;
        lines++;
      } else if (defaultSpecifier) {
        imported = defaultSpecifier;
        if (namedSpecifiers.length > 0) {
          imported += `, {${namedSpecifiers.join(', ')}}`;
        }
      } else if (namedSpecifiers.length > 0) {
        imported = `{${namedSpecifiers.join(', ')}}`;
      }

      if (imported.length > 0) {
        res += `import ${imported} from ${JSON.stringify(source)};\n`;
        lines++;
      } else if (!namespaceSpecifier) {
        res += `import ${JSON.stringify(source)};\n`;
        lines++;
      }
    }

    if (res.length > 0) {
      res += '\n';
      lines++;
    }

    return [res, lines];
  }

  buildBundlePostlude(): [string, number] {
    let res = '';
    let lines = 0;
    let exportSpecifiers = [];
    for (let {
      asset,
      exportSymbol,
      local,
      exportAs,
    } of this.packager.exportedSymbols.values()) {
      if (this.packager.wrappedAssets.has(asset.id)) {
        let obj = `parcelRequire("${this.packager.bundleGraph.getAssetPublicId(
          asset,
        )}")`;
        res += `\nvar ${local} = ${this.packager.getPropertyAccess(
          obj,
          exportSymbol,
        )};`;
        lines++;
      }

      for (let as of exportAs) {
        let specifier = local;
        if (exportAs !== local) {
          specifier += ` as ${as}`;
        }

        exportSpecifiers.push(specifier);
      }
    }

    if (exportSpecifiers.length > 0) {
      res += `\nexport {${exportSpecifiers.join(', ')}};`;
      lines++;
    }

    if (this.packager.shouldBundleQueue(this.packager.bundle)) {
      // Should be last thing the bundle executes on intial eval
      res += `\n$parcel$global.rlb(${JSON.stringify(
        this.packager.bundle.publicId,
      )})`;
      lines++;
    }

    return [res, lines];
  }
}