将 Array.prototype.includes 与 Typescript 一起使用时开玩笑测试失败？

Question

I started using Array.prototype.includes in this project:

https://github.com/fireflysemantics/validator

It is packaged using the Angular Package Format and the source is in this directory:

https://github.com/fireflysemantics/validator/tree/master/projects/validator

The project builds fine, however when the Jest tests are run this error occurs:

 FAIL  projects/validator/src/lib/decorators/IsDefined.spec.ts
  ● should create an error when using validate

    TypeError: Cannot read property 'includes' of undefined

      35 |   const mc: MetaClass = ValidationContainer.metaClasses.get(cn);
      36 |   if (mc) {
    > 37 |     const properties: string[] = mc.properties.filter(p => !exlude.includes(p))

So it seems as if Jest is not picking up the property typescript configuration, which does include:

    "lib": [
      "dom",
      "es2018"
    ]

Thoughts?

Answer 1

You are misinterpreting the error. It's not that includes is not allowed.

It's that it cannot access the property includes on a value that is undefined , ie apparently you try to do undefined.includes , so that would mean that exlude must be undefined .

---

In your IsDefined.spec.ts you are calling validate like this:

it(`should create an error when using validate`, ()=>{
  let IDI = new IsDefinedInvalid();
  let e = validate(IDI);
  expect(e.valid).toBeFalsy();
});

So, you are passing only 1 argument ( IDI ) to validate . However, in validate.ts you define the function like this:

export function validate(target: any, exlude?: string[]): ObjectErrors {
  let oes: ObjectErrors = new ObjectErrors();
  const cn: string = target.constructor.name;
  const mc: MetaClass = ValidationContainer.metaClasses.get(cn);
  if (mc) {
    const properties: string[] = mc.properties.filter(p => !exlude.includes(p))
    properties.forEach(p => {
      if (!validateProperty(target, p, oes)) {
        oes.valid = false;
      }
    });
  }
  return oes;
}

As you can see, validate takes two arguments - target and exlude . (By the way, that is misspelled and should be exclude with a c .) Yes, exlude as marked as optional with ? , so it's contractually OK that you omit it, however inside the validate function you then use exlude (in the line that crashed) without first checking whether it is undefined , so you end up calling undefined.includes(p) !

To be honest, I'm not sure why the TypeScript compiler isn't complaining at this point. (Maybe a commenter has an idea why...)

Anyway, the solution is to set a default value of [] in the function definition in validate.ts :

export function validate(target: any, exlude: string[] = []): ObjectErrors {

(Of course it would also work to pass the second argument as empty array when calling the function ( validate(IDI, []) ), but then the bug in validate will still exist.)