Anonymous functions

The JavaScript language also has the concept of anonymous functions. These are functions that are defined on the fly and don't specify a function name. Consider the following JavaScript code:

var addVar = function(a,b) { 
    return a + b; 
} 
 
var addVarResult = addVar(2,3); 
console.log("addVarResult:"" + addVarResult);

Here, we define a function that has no name and adds two values. Because the function does not have a name, it is known as an anonymous function. This anonymous function is then assigned to a variable named addVar. The addVar variable can then be invoked as a function with two parameters, and the return value will be the result of executing the anonymous function. The output of this code will be as follows:

addVarResult:5  

Let's now rewrite the preceding anonymous JavaScript function in TypeScript, as follows:

var addFunction = function(a:number, b:number) : number { 
    return a + b; 
} 
var addFunctionResult = addFunction(2,3); 
console.log(`addFunctionResult : ${addFunctionResult}`); 

Here, we see that TypeScript allows anonymous functions in the same way that JavaScript does, but also allows standard type annotations. The output of this TypeScript code is as follows:

addFunctionResult : 5