JavaScript function expression vs function statement

function expressions and function statements are very similar in JavaScript, the difference is how the browser loads them into the execution context.

// function statement
function foo() {
}

// function expression
var foo = function() {
};

<b>function statements</b>

A function statement loads before any code is executed. This behavior of function statements is called hoisting, which allows a function to be used before it is defined.

alert(foo()); // Alerts "hello from foo".
function foo() { return "hello from foo"; } 

<b>function expressions</b>

A function expression associates a value with a variable, just like any other assignment statement. function expressions load only when the interpreter reaches the definition of the function.

alert(foo()); // ERROR!
var foo = function() { return "hello from foo"; } 

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