JavaScript - function declaration vs function expression

In this article, we would like to show you the difference between function declaration and function expression in JavaScript.

Quick solution:

1. function myFunction() {} - is a function declaration,

2. var myFunction = function() {} - is a function expression.

In this section, we present the difference between function declaration and function expression in a practical example.

In this example, myFunction() is a function declaration and due to hoisting, it is defined whenever the surrounding function or script is executed.

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myFunction();  // Output: Hello World!

​

function myFunction() {

    console.log('Hello World!');

}

In this example, myFunction() is a function expression, that is defined only after reaching this line.

Example 1:

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myFunction(); // Output: Uncaught TypeError: myFunction is not a function

​

var myFunction = function() {

    console.log('Hello World!');

};

Example 2:

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myFunction(); // Output: Uncaught ReferenceError: Cannot access 'myFunction' before initialization

​

let myFunction = function() {

    console.log('Hello World!');

};

1. JavaScript - difference between let and var

1. Function declaration - JavaScript | MDN
2. Function expression - JavaScript | MDN