Function build

test/MagicString.test.ts:1155–1160

(s: MagicString)

      const original = 'const a = 1;\nconst b = 2;\n\nexport { a, b };\n'

      const build = (s: MagicString) => {
        s.prepend('// header\n')
        s.appendLeft(12, '\nconst inserted = 3;')
        s.overwrite(13, 25, 'const b = 20;\nconst c = 30;')
        s.append('// footer\n')
      }

      const generated = new MagicString(original)
      build(generated)