How to handle errors using Flow type hinting and Jest











up vote
3
down vote

favorite












I have a class defined like this:



class MyClass{
constructor(data:Array<any>){
...
}
}


And a basic test setup in Jest like this:



test('bad args', () => {
expect(new MyClass()).toThrow();
expect(new MyClass({})).toThrow();
expect(new MyClass('string')).toThrow();
});


I would expect these to error as the type hinting does not allow for empty constructor args and expects first arg to be array not an object or string.



Can anyone help explain how I persuade Jest to run the code through Flow and error where types are incorrect?



EDIT:
I also have run flow-typed install jest@23.6.0 //correct jest version










share|improve this question




























    up vote
    3
    down vote

    favorite












    I have a class defined like this:



    class MyClass{
    constructor(data:Array<any>){
    ...
    }
    }


    And a basic test setup in Jest like this:



    test('bad args', () => {
    expect(new MyClass()).toThrow();
    expect(new MyClass({})).toThrow();
    expect(new MyClass('string')).toThrow();
    });


    I would expect these to error as the type hinting does not allow for empty constructor args and expects first arg to be array not an object or string.



    Can anyone help explain how I persuade Jest to run the code through Flow and error where types are incorrect?



    EDIT:
    I also have run flow-typed install jest@23.6.0 //correct jest version










    share|improve this question


























      up vote
      3
      down vote

      favorite









      up vote
      3
      down vote

      favorite











      I have a class defined like this:



      class MyClass{
      constructor(data:Array<any>){
      ...
      }
      }


      And a basic test setup in Jest like this:



      test('bad args', () => {
      expect(new MyClass()).toThrow();
      expect(new MyClass({})).toThrow();
      expect(new MyClass('string')).toThrow();
      });


      I would expect these to error as the type hinting does not allow for empty constructor args and expects first arg to be array not an object or string.



      Can anyone help explain how I persuade Jest to run the code through Flow and error where types are incorrect?



      EDIT:
      I also have run flow-typed install jest@23.6.0 //correct jest version










      share|improve this question















      I have a class defined like this:



      class MyClass{
      constructor(data:Array<any>){
      ...
      }
      }


      And a basic test setup in Jest like this:



      test('bad args', () => {
      expect(new MyClass()).toThrow();
      expect(new MyClass({})).toThrow();
      expect(new MyClass('string')).toThrow();
      });


      I would expect these to error as the type hinting does not allow for empty constructor args and expects first arg to be array not an object or string.



      Can anyone help explain how I persuade Jest to run the code through Flow and error where types are incorrect?



      EDIT:
      I also have run flow-typed install jest@23.6.0 //correct jest version







      javascript jestjs flowtype






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Nov 8 at 10:57

























      asked Nov 8 at 10:41









      Mike Miller

      2,04611220




      2,04611220
























          1 Answer
          1






          active

          oldest

          votes

















          up vote
          1
          down vote



          accepted










          The doc states that:




          Babel will take your Flow code and strip out any type annotations.




          So, flow can help you to find wrong call before build (usually at development time, in ide). And once you run flow in your project - you can catch where is signature mismatch.



          After compiling flow annotations are removed, and you have pure javascript.



          So, if your constructor accepts any arg, but only array is valid one, you can explicitly state that:



          class MyClass {
          constructor(data:*) {
          if (!Array.isArray(data)) {
          throw new Exception('Bad argument');
          }
          }
          }


          The above codebase will work if you specify data:Array<any> as well, but you'll see errors at compiling time (so you can catch who to blame :) ).






          share|improve this answer





















          • Thanks, that makes perfect sense - hadn't thought it through properly
            – Mike Miller
            Nov 8 at 14:59











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          1 Answer
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          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes








          up vote
          1
          down vote



          accepted










          The doc states that:




          Babel will take your Flow code and strip out any type annotations.




          So, flow can help you to find wrong call before build (usually at development time, in ide). And once you run flow in your project - you can catch where is signature mismatch.



          After compiling flow annotations are removed, and you have pure javascript.



          So, if your constructor accepts any arg, but only array is valid one, you can explicitly state that:



          class MyClass {
          constructor(data:*) {
          if (!Array.isArray(data)) {
          throw new Exception('Bad argument');
          }
          }
          }


          The above codebase will work if you specify data:Array<any> as well, but you'll see errors at compiling time (so you can catch who to blame :) ).






          share|improve this answer





















          • Thanks, that makes perfect sense - hadn't thought it through properly
            – Mike Miller
            Nov 8 at 14:59















          up vote
          1
          down vote



          accepted










          The doc states that:




          Babel will take your Flow code and strip out any type annotations.




          So, flow can help you to find wrong call before build (usually at development time, in ide). And once you run flow in your project - you can catch where is signature mismatch.



          After compiling flow annotations are removed, and you have pure javascript.



          So, if your constructor accepts any arg, but only array is valid one, you can explicitly state that:



          class MyClass {
          constructor(data:*) {
          if (!Array.isArray(data)) {
          throw new Exception('Bad argument');
          }
          }
          }


          The above codebase will work if you specify data:Array<any> as well, but you'll see errors at compiling time (so you can catch who to blame :) ).






          share|improve this answer





















          • Thanks, that makes perfect sense - hadn't thought it through properly
            – Mike Miller
            Nov 8 at 14:59













          up vote
          1
          down vote



          accepted







          up vote
          1
          down vote



          accepted






          The doc states that:




          Babel will take your Flow code and strip out any type annotations.




          So, flow can help you to find wrong call before build (usually at development time, in ide). And once you run flow in your project - you can catch where is signature mismatch.



          After compiling flow annotations are removed, and you have pure javascript.



          So, if your constructor accepts any arg, but only array is valid one, you can explicitly state that:



          class MyClass {
          constructor(data:*) {
          if (!Array.isArray(data)) {
          throw new Exception('Bad argument');
          }
          }
          }


          The above codebase will work if you specify data:Array<any> as well, but you'll see errors at compiling time (so you can catch who to blame :) ).






          share|improve this answer












          The doc states that:




          Babel will take your Flow code and strip out any type annotations.




          So, flow can help you to find wrong call before build (usually at development time, in ide). And once you run flow in your project - you can catch where is signature mismatch.



          After compiling flow annotations are removed, and you have pure javascript.



          So, if your constructor accepts any arg, but only array is valid one, you can explicitly state that:



          class MyClass {
          constructor(data:*) {
          if (!Array.isArray(data)) {
          throw new Exception('Bad argument');
          }
          }
          }


          The above codebase will work if you specify data:Array<any> as well, but you'll see errors at compiling time (so you can catch who to blame :) ).







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 8 at 14:51









          Alex

          2,787620




          2,787620












          • Thanks, that makes perfect sense - hadn't thought it through properly
            – Mike Miller
            Nov 8 at 14:59


















          • Thanks, that makes perfect sense - hadn't thought it through properly
            – Mike Miller
            Nov 8 at 14:59
















          Thanks, that makes perfect sense - hadn't thought it through properly
          – Mike Miller
          Nov 8 at 14:59




          Thanks, that makes perfect sense - hadn't thought it through properly
          – Mike Miller
          Nov 8 at 14:59


















           

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