class C {x!}

class C {x! = 1}

> require('oxc-parser').parseSync('1.ts','class A {x!}',{}).errors
[
  {
    severity: 'Error',
    message: 'Declarations with definite assignment assertions must also have type annotations.',
    labels: [ [Object] ],
    helpMessage: null,
    codeframe: '\n' +
      '  x TS(1264): Declarations with definite assignment assertions must also have\n' +
      '  | type annotations.\n' +
      '   ,-[1.ts:1:11]\n' +
      ' 1 | class A {x!}\n' +
      '   :           ^\n' +
      '   `----\n'
  }
]
> require('oxc-parser').parseSync('1.ts','class A {x! = 1}',{}).errors
[
  {
    severity: 'Error',
    message: 'Declarations with initializers cannot also have definite assignment assertions.',
    labels: [ [Object] ],
    helpMessage: null,
    codeframe: '\n' +
      '  x TS(1263): Declarations with initializers cannot also have definite\n' +
      '  | assignment assertions.\n' +
      '   ,-[1.ts:1:11]\n' +
      ' 1 | class A {x! = 1}\n' +
      '   :           ^\n' +
      '   `----\n'
  }
]