Let's take a look at two interfaces, A and B:
interface A {f(): number}
interface B {f: () => number}
I have experimented with the following:
var a: A = {f: function() {return 1}}
var a: A = {f: () => 1}
var b: B = {f: function() {return 1}}
var b: B = {f: () => 1}
It seems like they are essentially the same.
Both expressions are equivalent as they represent the same concept in different notations. According to your interfaces, there is a requirement for a property f, which should be a function that returns a number without any parameters.
The implementations {f: function() {return 1}} and {f: () => 1} achieve the same goal but use different syntax. The latter makes use of an arrow function, which offers a more concise way to define functions. While it may seem like just syntactic sugar, it does have a slight variation in behavior when it comes to the usage of the this keyword.
Here's a breakdown:
interface A { f(): number }
Represents the syntax for defining a method, whereas this:
interface B { f: () => number }
Demonstrates how to declare a property with a function type.
Although there isn't much distinction in interfaces, it becomes clearer in a class scenario:
class MyNewClass {
myMethod1() {
return 0;
}
myMethod2 = () => {
return 0;
}
myMethod3 = function () {
return 0;
}
}
The compilation results in:
var MyNewClass = (function () {
function MyNewClass() {
this.myMethod2 = function () {
return 0;
};
this.myMethod3 = function () {
return 0;
};
}
MyNewClass.prototype.myMethod1 = function () {
return 0;
};
return MyNewClass;
}());
It's evident that only myMethod1 is a method linked to the prototype, while the other two are simply properties assigned within the constructor.
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