An object is an instance which contains set of key value pairs. The values can be scalar values or functions or even array of other objects. The syntax is given below −
The output of the above code is as follows −
You can solve this by using a method template in declaration.
The output of the above code is as follows −
On compiling, it will generate following JavaScript code.
“When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck.”
The TypeScript compiler implements the duck-typing system that allows object creation on the fly while keeping type safety. The following example shows how we can pass objects that don’t explicitly implement an interface but contain all of the required members to a function.
Syntax
var object_name = { key1: “value1”, //scalar value key2: “value”, key3: function() { //functions }, key4:[“content1”, “content2”] //collection };As shown above, an object can contain scalar values, functions and structures like arrays and tuples.
Example: Object Literal Notation
var person = { firstname:"Tom", lastname:"Hanks" }; //access the object values console.log(person.firstname) console.log(person.lastname)On compiling, it will generate the same code in JavaScript.
The output of the above code is as follows −
Tom Hanks
TypeScript Type Template
Let’s say you created an object literal in JavaScript as −var person = { firstname:"Tom", lastname:"Hanks" };In case you want to add some value to an object, JavaScript allows you to make the necessary modification. Suppose we need to add a function to the person object later this is the way you can do this.
person.sayHello = function(){ return "hello";}If you use the same code in Typescript the compiler gives an error. This is because in Typescript, concrete objects should have a type template. Objects in Typescript must be an instance of a particular type.
You can solve this by using a method template in declaration.
Example: Typescript Type template
var person = { firstName:"Tom", lastName:"Hanks", sayHello:function() { } //Type template } person.sayHello = function() { console.log("hello "+person.firstName) } person.sayHello()On compiling, it will generate the same code in JavaScript.
The output of the above code is as follows −
hello TomObjects can also be passed as parameters to function.
Example: Objects as function parameters
var person = { firstname:"Tom", lastname:"Hanks" }; var invokeperson = function(obj: { firstname:string, lastname :string }) { console.log("first name :"+obj.firstname) console.log("last name :"+obj.lastname) } invokeperson(person)The example declares an object literal. The function expression is invoked passing person object.
On compiling, it will generate following JavaScript code.
//Generated by typescript 1.8.10 var person = { firstname: "Tom", lastname: "Hanks" }; var invokeperson = function (obj) { console.log("first name :" + obj.firstname); console.log("last name :" + obj.lastname); }; invokeperson(person);Its output is as follows −
first name :Tom last name :HanksYou can create and pass an anonymous object on the fly.
Example: Anonymous Object
var invokeperson = function(obj:{ firstname:string, lastname :string}) { console.log("first name :"+obj.firstname) console.log("last name :"+obj.lastname) } invokeperson({firstname:"Sachin",lastname:"Tendulkar"});On compiling, it will generate following JavaScript code.
//Generated by typescript 1.8.10 var invokeperson = function (obj) { console.log("first name :" + obj.firstname); console.log("last name :" + obj.lastname); }; invokeperson({ firstname: "Sachin", lastname: "Tendulkar" }); invokeperson({ firstname: "Sachin", lastname: "Tendulkar" });Its output is as follows −
first name :Sachin last name :Tendulkar
Duck-typing
In duck-typing, two objects are considered to be of the same type if both share the same set of properties. Duck-typing verifies the presence of certain properties in the objects, rather than their actual type, to check their suitability. The concept is generally explained by the following phrase −“When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck.”
The TypeScript compiler implements the duck-typing system that allows object creation on the fly while keeping type safety. The following example shows how we can pass objects that don’t explicitly implement an interface but contain all of the required members to a function.
Example
interface IPoint { x:number y:number } function addPoints(p1:IPoint,p2:IPoint):IPoint { var x = p1.x + p2.x var y = p1.y + p2.y return {x:x,y:y} } //Valid var newPoint = addPoints({x:3,y:4},{x:5,y:1}) //Error var newPoint2 = addPoints({x:1},{x:4,y:3})
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