classgen.js

const className = 'StateId'
const interfaceName = 'StateIdInterface'
const data = `  state: string;
  value: string;
  isActive: boolean;
  toJSON(): { [key: string]: any };`

const members = data
  .replace(/\n/g, '')
  .split(';')
  .filter(l => l)
  .map(l => {
    const [, name, type] = l.trim().match('(.*?):(.*)$')

    return {
      name: name.trim(), 
      type: type.trim()
    }
  })

  const privateMembers = members
    .filter(m => !m.name.endsWith('()'))
    .map(m => `private _${m.name}: ${m.type};`)
    .join('\n')

  const constructorParameters = members
    .filter(m => !m.name.endsWith('()'))
    .map(m => `${m.name}: ${m.type}`)
    .join(', ')

  const constructorAssignments = members
    .filter(m => !m.name.endsWith('()'))
    .map(m => `this._${m.name} = ${m.name};`)
    .join('\n')

  const getters = members
    .filter(m => !m.name.endsWith('()'))
    .map(m => `get ${m.name}() { return this._${m.name} };`)
    .join('\n\n')

  const methodDeclarations = members
    .filter(m => m.name.endsWith('()'))
    .map(m => `${m.name}: ${m.type} { throw new Error('Not Implemented') };`)
    .join('\n')

  const clazz = `
    export class ${className} implements ${interfaceName} {
      ${privateMembers}

      constructor(${constructorParameters}) {
        ${constructorAssignments}
      }

      ${getters}

      ${methodDeclarations}
    }
  `

  console.log(clazz.trim())