[Javascript]Function Expression vs Function Declaration

❗️ Defferences

Function Declaration

• A Function Declaration can be called earlier than it is defined.
• When JavaScript prepares to run the script, it first looks for global Function Declarations in it and creates the functions - hoisting

sayHi("John"); // Hello, John 

function sayHi(name) {
  alert( `Hello, ${name}` );
}

• When a Function Declaration is within a code block, it’s visible everywhere inside that block. But not outside of it - Block Scope

let age = prompt("What is your age?", 18);

// conditionally declare a function
if (age < 18) {

  function welcome() {
    alert("Hello!");
  }

} else {

  function welcome() {
    alert("Greetings!");
  }
}

// ...use it later
welcome(); // Error: welcome is not defined

Function Expresstion

• A Function Expression is created when the execution reaches it - Prevent to pollute the global scope

sayHi("John"); // error!

let sayHi = function(name) {  // (*) no magic any more
  alert( `Hello, ${name}` );
};