TypeScript Objects as Dictionary types as in C

Question

I have some JavaScript code that uses objects as dictionaries  for example a  person  object will hold a some personal details keyed off the email address   var people     lt email gt     lt  some personal data  gt     adding    gt   people  lt email gt      lt data gt     getting   gt   var data   people  lt email gt      deleting  gt   delete people  lt email gt       Is it possible to describe this in Typescript  or do I have to use an Array

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You can also use the Record type in typescript    export interface nameInterface        propName   Record lt string  otherComplexInterface gt

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You can use Record for this   https   www typescriptlang org docs handbook utility-types html recordkt  Example  A mapping between AppointmentStatus enum and some meta data      const iconMapping  Record lt AppointmentStatus  Icon gt           AppointmentStatus Failed     Name   calendar times   Color   red          AppointmentStatus Canceled     Name   calendar times outline   Color   red          AppointmentStatus Confirmed     Name   calendar check outline   Color   green          AppointmentStatus Requested     Name   calendar alternate outline   Color   orange          AppointmentStatus None     Name   calendar outline   Color   blue          Now with interface as value    interface Icon     Name  string   Color  string    Usage   const icon  SemanticIcon   iconMapping appointment Status

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Lodash has a simple Dictionary implementation and has good TypeScript support  Install Lodash   npm install lodash  types lodash --save   Import and usage   import   Dictionary   from  lodash   let properties   Dictionary lt string gt           key    value            console log properties  key

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You can use templated interfaces like this    interface Map lt T gt         K  string   T     let dict  Map lt number gt        dict  one     1

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In addition to using an map-like object  there has been an actual Map object for some time now  which is available in TypeScript when compiling to ES6  or when using a polyfill with the ES6 type-definitions   let people   new Map lt string  Person gt       It supports the same functionality as Object  and more  with a slightly different syntax      Adding an item  a key-value pair   people set  John     firstName   John   lastName   Doe          Checking for the presence of a key  people has  John       true     Retrieving a value by a key  people get  John   lastName      Doe      Deleting an item by a key  people delete  John      This alone has several advantages over using a map-like object  such as    Support for non-string based keys  e g  numbers or objects  neither of which are supported by Object  no  Object does not support numbers  it converts them to strings  Less room for errors when not using --noImplicitAny  as a Map always has a key type and a value type  whereas an object might not have an index-signature The functionality of adding removing items  key-value pairs  is optimized for the task  unlike creating properties on an Object   Additionally  a Map object provides a more powerful and elegant API for common tasks  most of which are not available through simple Objects without hacking together helper functions  although some of these require a full ES6 iterator iterable polyfill for ES5 targets or below       Iterate over Map entries  people forEach  person  key    gt            Clear the Map  people clear        Get Map size  people size      Extract keys into array  in insertion order   let keys   Array from people keys         Extract values into array  in insertion order   let values   Array from people values

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In newer versions of typescript you can use   type Customers   Record lt string  Customer gt    In older versions you can use   var map     email  string   Customer           map  foo gmail com     new Customer       OK map 14    new Customer       Not OK  14 is not a string map  bar hotmail com      x      Not OK   x  is not a customer   You can also make an interface if you don t want to type that whole type annotation out every time   interface StringToCustomerMap        email  string   Customer     var map  StringToCustomerMap           Equivalent to first line of above

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