TypeScript相当于JavaScript包括（）

Question

Getting a TypeScript error using includes on an array element. Of course once compiled down to js it works fine but I still get the following TypeScript error:

Property 'includes' does not exist on type 'boolean[]'

Code:

validAttrs() {
  let valid: boolean[] = this.required.map((value, index) => {
    if(this.elm.nativeElement.getAttribute(value) === null) {
      return false;
    };
    return true;
  });
  return valid.includes(false) ? false : true;
}

Answer 1

As far as fixing the compilation error goes, fixed the compilation issue was adding es2016 to the lib option in my tsconfig.json . This adds the necessary declaration of includes on arrays.

I tried with TypeScript 2.1.4 the suggested fix of replacing boolean[] with Array<boolean> . It made no difference whatsoever. Logically, it shouldn't make a difference because boolean[] and Array<boolean> are the same thing .

---

This being said, I concur with torazaburo that the OP's code should be implemented as:

validAttrs() {
  return this.required.every(value => this.elm.nativeElement.getAttribute(value) !== null);
}

Besides removing unnecessary logic, this also has the advantage that every stops inspecting the array as soon as the callback returns a falsy value. There's no point inspecting the rest because the return value will necessarily be false as soon as the callback returns a falsy value. On the other hand, the implementation in the question will always perform the test on all elements the of array. If the very first element fails the test, then it will inspect the rest of the array needlessly!!

Answer 2

@echonax's comment worked for me.

validAttrs() {
  let valid: Array<boolean> = this.required.map((value, index) => {
    if(this.elm.nativeElement.getAttribute(value) === null) {
      return false;
    };
    return true;
  });
  return valid.includes(false) ? false : true;
}

Answer 3

You don't even need includes for what you are trying to do. Your code can simply be

validAttrs() {
  return this.required.every(value => this.elm.nativeElement.getAttribute(value) !== null);
}

This also has the advantage that it will stop checking the minute it finds the first null value.