JavaScript

Function Expression allows us to create an anonymous function which doesn’t have any function name which is the main difference between Function Expression and Function Declaration. A function expression can be used as an IIFE (Immediately Invoked Function Expression)which runs as soon as it is defined. A function expression has to be stored in a variable and can be accessed using variableName. With the ES6 features introducing Arrow Function, it becomes more easier to declare function expression.

Syntax for Function Declaration:

function functionName(x, y) { statements... return (z) };

Syntax for Function Expression (anonymous) :

let variableName = function(x, y) { statements... return (z) };

Syntax for Function Expression (named) :

let variableName = function functionName(x, y) 
{ statements... return (z) };

Syantax for Arrow Function:

let variableName = (x, y) => { statements... return (z) };

Note:

A function expression has to be defined first before calling it or using it as a parameter.
An arrow function must have an return statement.

Below examples illustrate the funcion expression in JavaScript:

Example 1: Code for Function Declaration.

<script> 
    function callAdd(x, y){ 
        let z = x + y; 
        return z;     
    }  
    console.log("Addition : " + callAdd(7, 4)); 
</script>

Output:

Addition : 11

Example 2: Code for Function Expression (anonymous)

Javascript

<script> 
    var calSub = function(x, y){ 
        let z = x - y; 
        return z; 
    } 
  
    console.log("Subtration : " + calSub(7, 4)); 
 </script>

Output:

Subtration : 3

Example 3: Code for Function Expression (named)

Javascript

<script> 
    var calMul = function Mul(x, y){ 
        let z = x * y; 
        return z; 
    } 
  
    console.log("Multiplication : " + calMul(7, 4)); 
</script>

Output:

Multiplication : 28

Example 4: Code for Arrow Function

Javascript

<script> 
    var calDiv = (x, y) => { 
        let z = x / y; 
        return z; 
    } 
  
    console.log("Division : " + calDiv(24, 4)); 
</script>

Output:

Division : 6

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