Typescript can i use generic type in function body










1















i have function declaration like this:



export const filterOptions: <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) => OptionsArray<OptionValueType> = (options, filterBy) => 
if (filterBy === '')
return [...options];
else
const filteredOptions: OptionsArray<OptionValueType> = ;
// filter and return options


return [...filteredOptions];

;


but, typescript mark this code as Error, can we use generic types in function body ?



const filteredOptions: OptionsArray<OptionValueType> = ;


TS2304: Cannot find name 'OptionValueType'










share|improve this question


























    1















    i have function declaration like this:



    export const filterOptions: <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) => OptionsArray<OptionValueType> = (options, filterBy) => 
    if (filterBy === '')
    return [...options];
    else
    const filteredOptions: OptionsArray<OptionValueType> = ;
    // filter and return options


    return [...filteredOptions];

    ;


    but, typescript mark this code as Error, can we use generic types in function body ?



    const filteredOptions: OptionsArray<OptionValueType> = ;


    TS2304: Cannot find name 'OptionValueType'










    share|improve this question
























      1












      1








      1


      0






      i have function declaration like this:



      export const filterOptions: <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) => OptionsArray<OptionValueType> = (options, filterBy) => 
      if (filterBy === '')
      return [...options];
      else
      const filteredOptions: OptionsArray<OptionValueType> = ;
      // filter and return options


      return [...filteredOptions];

      ;


      but, typescript mark this code as Error, can we use generic types in function body ?



      const filteredOptions: OptionsArray<OptionValueType> = ;


      TS2304: Cannot find name 'OptionValueType'










      share|improve this question














      i have function declaration like this:



      export const filterOptions: <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) => OptionsArray<OptionValueType> = (options, filterBy) => 
      if (filterBy === '')
      return [...options];
      else
      const filteredOptions: OptionsArray<OptionValueType> = ;
      // filter and return options


      return [...filteredOptions];

      ;


      but, typescript mark this code as Error, can we use generic types in function body ?



      const filteredOptions: OptionsArray<OptionValueType> = ;


      TS2304: Cannot find name 'OptionValueType'







      typescript






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      share|improve this question










      asked Nov 15 '18 at 13:10









      Евгений ЛитвиненкоЕвгений Литвиненко

      2915




      2915






















          1 Answer
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          You can use the generic type parameter in the body, but the generic type parameter has to be on the function implementation not on the variable that will hold the function



          export const filterOptions = <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) : OptionsArray<OptionValueType> => 
          if (filterBy === '')
          return [...options];
          else
          const filteredOptions: OptionsArray<OptionValueType> = ;
          // filter and return options


          return [...filteredOptions];

          ;





          share|improve this answer


















          • 1





            You save my day! Thank you.

            – Евгений Литвиненко
            Nov 15 '18 at 14:21










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          You can use the generic type parameter in the body, but the generic type parameter has to be on the function implementation not on the variable that will hold the function



          export const filterOptions = <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) : OptionsArray<OptionValueType> => 
          if (filterBy === '')
          return [...options];
          else
          const filteredOptions: OptionsArray<OptionValueType> = ;
          // filter and return options


          return [...filteredOptions];

          ;





          share|improve this answer


















          • 1





            You save my day! Thank you.

            – Евгений Литвиненко
            Nov 15 '18 at 14:21















          0














          You can use the generic type parameter in the body, but the generic type parameter has to be on the function implementation not on the variable that will hold the function



          export const filterOptions = <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) : OptionsArray<OptionValueType> => 
          if (filterBy === '')
          return [...options];
          else
          const filteredOptions: OptionsArray<OptionValueType> = ;
          // filter and return options


          return [...filteredOptions];

          ;





          share|improve this answer


















          • 1





            You save my day! Thank you.

            – Евгений Литвиненко
            Nov 15 '18 at 14:21













          0












          0








          0







          You can use the generic type parameter in the body, but the generic type parameter has to be on the function implementation not on the variable that will hold the function



          export const filterOptions = <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) : OptionsArray<OptionValueType> => 
          if (filterBy === '')
          return [...options];
          else
          const filteredOptions: OptionsArray<OptionValueType> = ;
          // filter and return options


          return [...filteredOptions];

          ;





          share|improve this answer













          You can use the generic type parameter in the body, but the generic type parameter has to be on the function implementation not on the variable that will hold the function



          export const filterOptions = <OptionValueType>(options: OptionsArray<OptionValueType>, filterBy: string) : OptionsArray<OptionValueType> => 
          if (filterBy === '')
          return [...options];
          else
          const filteredOptions: OptionsArray<OptionValueType> = ;
          // filter and return options


          return [...filteredOptions];

          ;






          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered Nov 15 '18 at 13:54









          Titian Cernicova-DragomirTitian Cernicova-Dragomir

          70.2k34866




          70.2k34866







          • 1





            You save my day! Thank you.

            – Евгений Литвиненко
            Nov 15 '18 at 14:21












          • 1





            You save my day! Thank you.

            – Евгений Литвиненко
            Nov 15 '18 at 14:21







          1




          1





          You save my day! Thank you.

          – Евгений Литвиненко
          Nov 15 '18 at 14:21





          You save my day! Thank you.

          – Евгений Литвиненко
          Nov 15 '18 at 14:21



















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