any vs Object

Question

I am looking at TypeScript code and noticed that they use   interface Blablabla       field  Object       What is the benefit of using Object vs any  as in   interface Blablabla      field  any

User · Answer

Contrary to  NET where all types derive from an  object   in TypeScript  all types derive from  any   I just wanted to add this comparison as I think it will be a common one made as more  NET developers give TypeScript a try

User · Answer

Bit old  but doesn t hurt to add some notes   When you write something like this  let a  any  let b  Object  let c         a has no interface  it can be anything  the compiler knows nothing about its members so no type checking is performed when accessing assigning both to it and its members  Basically  you re telling the compiler to  back off  I know what I m doing  so just trust me   b has the Object interface  so ONLY the members defined in that interface are available for b  It s still JavaScript  so everything extends Object  c extends Object  like anything else in TypeScript  but adds no members  Since type compatibility in TypeScript is based on structural subtyping  not nominal subtyping  c ends up being the same as b because they have the same interface  the Object interface    And that s why  a doSomething       Ok  the compiler trusts you on that b doSomething       Error  Object has no doSomething member c doSomething       Error  c neither has doSomething nor inherits it from Object   and why  a toString       Ok  whatever  dude  have it your way b toString       Ok  toString is defined in Object c toString       Ok  c inherits toString from Object   So Object and    are equivalents in TypeScript   If you declare functions like these  function fa param  any   void    function fb param  Object   void      with the intention of accepting anything for param  maybe you re going to check types at run-time to decide what to do with it   remember that   inside fa  the compiler will let you do whatever you want with param  inside fb  the compiler will only let you reference Object s members    It is worth noting  though  that if param is supposed to accept multiple known types  a better approach is to declare it using union types  as in  function fc param  string number   void      Obviously  OO inheritance rules still apply  so if you want to accept instances of derived classes and treat them based on their base type  as in  interface IPerson       gender  string     class Person implements IPerson       gender  string     class Teacher extends Person     function func person  IPerson   void       console log person gender      func new Person            Ok func new Teacher           Ok func  gender   male        Ok func  name   male          Error  no gender     the base type is the way to do it  not any  But that s OO  out of scope  I just wanted to clarify that any should only be used when you don t know whats coming  and for anything else you should annotate the correct type   UPDATE   Typescript 2 2 added an object type  which specifies that a value is a non-primitive   i e  not a number  string  boolean  symbol  undefined  or null    Consider functions defined as   function b x  Object     function c x         function d x  object       x will have the same available properties within all of these functions  but it s a type error to call d with a primitive   b  foo      Okay c  foo      Okay d  foo      Error   foo  is a primitive

User · Answer

Adding to Alex s answer and simplifying it   Objects are more strict with their use and hence gives the programmer more compile time  evaluation  power and hence in a lot of cases provide more  checking capability  and coould prevent any leaks  whereas any is a more generic term and a lot of compile time checks might hence be ignored

User · Answer

any is something specific to TypeScript is explained quite well by alex s answer    Object refers to the JavaScript object type  Commonly used as    or sometimes new Object  Most things in javascript are compatible with the object data type as they inherit from it  But any is TypeScript specific and compatible with everything in both directions  not inheritance based   e g      var foo Object   var bar any  var num number   foo   num     Not an error num   foo     ERROR      Any is compatible both ways  bar   num  num   bar

User · Answer

Object is more restrictive than any  For example    let a  any  let b  Object   a nomethod       Transpiles just fine b nomethod       Error  Property  nomethod  does not exist on type  Object     The Object class does not have a nomethod   function  therefore the transpiler will generate an error telling you exactly that  If you use any instead you are basically telling the transpiler that anything goes  you are providing no information about what is stored in a - it can be anything  And therefore the transpiler will allow you to do whatever you want with something defined as any   So in short   any can be anything  you can call any method etc on it without compilation errors  Object exposes the functions and properties defined in the Object class

User · Answer

Object appears to be a more specific declaration than any  From the TypeScript spec  section 3       All types in TypeScript are subtypes of a single top type called the   Any type  The any keyword references  this type  The Any type is the   one type that can represent any JavaScript value with no constraints    All  other types are categorized as primitive types  object types  or   type parameters  These types introduce  various static constraints on   their values    Also      The Any type is used to represent any JavaScript value  A value of the   Any type supports the same  operations as a value in JavaScript and   minimal static type checking is performed for operations on Any    values  Specifically  properties of any name can be accessed through   an Any value and Any values can be  called as functions or   constructors with any argument list    Objects do not allow the same flexibility    For example   var myAny   any   myAny Something       no problemo  var myObject   Object   myObject Something       Error  The property  Something  does not exist on value of type  Object

[typescript] 'any' vs 'Object'

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