JavaScript: Moving to ES2015

Function declarations versus function expressions

We saw two ways by which functions are defined. Though they both serve identical purposes, there is a difference between these two types of declarations. Check the following example:

//Function expression
functionOne();
//Error
//"TypeError: functionOne is not a function

var functionOne = function() {
  console.log("functionOne");
};
//Function declaration
functionTwo();
//No error
//Prints - functionTwo

function functionTwo() {
  console.log("functionTwo");
}

A function declaration is processed when execution enters the context in which it appears before any step-by-step code is executed. The function that it creates is given a proper name (functionTwo() in the preceding example) and this name is put ...