JavaScript Function Expression

The Javascript Function Expression is used to define a function inside any expression. The Function Expression allows us to create an anonymous function that 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) };

Syntax 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 a return statement.

The below examples illustrate the function expression in JavaScript:

Example 1: Code for Function Declaration.

Javascript

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

Output: 

Addition : 11

Example 2: Code for Function Expression (anonymous) 

Javascript

let calSub = function (x, y) {
    let z = x - y;
    return z;
}

console.log("Subtraction : " + calSub(7, 4));

Output: 

Subtraction : 3

Example 3: Code for Function Expression (named) 

Javascript

let calMul = function Mul(x, y) {
    let z = x * y;
    return z;
}

console.log("Multiplication : " + calMul(7, 4));

Output:

Multiplication : 28

Example 4: Code for Arrow Function

Javascript

let calDiv = (x, y) => {
    let z = x / y;
    return z;
}

console.log("Division : " + calDiv(24, 4));

Output: 

Division : 6

We have a complete list of Javascript Functions, to check those please go through the Javascript Function Complete Reference article.

Supported Browser:

• Chrome 1 and above
• Edge 12 and above
• Firefox 1 and above
• Internet Explorer 3 and above
• Opera 3 and above
• Safari 1 and above