By 06/07/2015 18 Comments

Duck-Typing In TypeScript


  • Duck-Typing is a method/rule for checking the type compatibility for more complex variable types.
  • TypeScript compiler uses the duck-typing method to compare one object with other object by comparing that the both objects have the same type matching properties/variables names or not. If both objects are different from one another and have different property names then the TypeScript compiler will generates the compile-time error through the duck-typing method/rule.
  • Duck-typing feature gives type safety in TypeScript code.
  • Through the duck-typing rule TypeScript compiler checks that an object is same as other object or not.
  • According to duck-typing method, the both objects must have matching same properties/variables types.
  • Duck-typing is a powerful feature which brings strong typing concepts in TypeScript code.


// Following is an object creation with different properties and it is assigned to a local variable bookList
var bookList = { book: "C#", id: 1 };

/* In following statements re-assigning another object with same properties to bookList variable. Notice each new object declaration has same properties as well as also a new property. This is possible through duck-typing rule. */

bookList = { book: "TypeScript", id: 2, price: 1000 };
bookList = { book: "", id: 3, price: 2000, isbn: 2054 };

document.write("Book: " + + " <br/>");
document.write("Id: " +;

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