Defining array with multiple types in TypeScript

Question

I have an array of the form    1   message      How would I define this in TypeScript

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If you re treating it as a tuple  see section 3 3 3 of the language spec   then   var t  number  string     1   message     or  interface NumberStringTuple extends Array lt string number gt  0 number  1 string  var t NumberStringTuple    1   message

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Defining array with multiple types in TypeScript   Use a union type  string number    demo    const foo   string number        1   message          I have an array of the form    1   message       If you are sure that there are always only two elements  number  string  then you can declare it as a tuple    const foo   number  string      1   message

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You can either use a regular tuple interface IReqularDemo   number  string    or if optional parameters support is needed interface IOptionalDemo   value1  number  value2   string

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I ve settled on the following format for typing arrays that can have items of multiple types   Array lt ItemType1   ItemType2   ItemType3 gt   This works well with testing and type guards  https   www typescriptlang org docs handbook advanced-types html type-guards-and-differentiating-types  This format doesn t work well with testing or type guards    ItemType1   ItemType2   ItemType3

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If you are interested in getting an array of either numbers or strings  you could define a type that will take an array of either type Tuple   Array lt number   string gt  const example  Tuple    1   quot message quot   const example2  Tuple     quot message quot   1   If you expect an array of a specific order  i e  number and a string  type Tuple    number  string  const example  Tuple    1   quot message quot   const example2  Tuple     quot messsage quot   1     Type  string  is not assignable to type  number

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My TS lint was complaining about other solutions  so the solution that was working for me was   item  Array lt Type1   Type2 gt    if there s only one type  it s fine to use   item  Type1

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TypeScript 3 9  update  May 12  2020  Now  TypeScript also supports named tuples  This greatly increases the understandability and maintainability of the code  Check the official TS playground   So  now instead of unnamed  const a   number  string      1   quot message quot      We can add names  const b   id  number  message  string      1   quot message quot       Note  you need to add all names at once  you can not omit some names  e g  type tIncorrect    id  number  string      INCORRECT  2nd element has no name  compile-time error  type tCorrect    id  number  msg  string      CORRECT  all have a names   Tip  if you are not sure in the count of the last elements  you can write it like this  type t    msg  string     indexes  number     means first element is a message and there are unknown number of indexes

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Im using this version   exampleArr  Array lt   id  number  msg  string  gt           id  1  msg   message         id  2  msg   message2        It is a little bit similar to the other suggestions but still easy and quite good to remember

[arrays] Defining array with multiple types in TypeScript

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