JavaScriptHoisting

// 1. Attempt to use "a" which is not declared in the body of the function
(function(){
    consloe.log(a); // this expression statements throws an exception
})();

VM78:3 Uncaught ReferenceError: consloe is not defined(…)


// 2. No error, but the variable is undefined. It gets hoisted to the top.
(function(){
    console.log(a); // a exists but it is undefined
    var a = 5;
})();

VM81:3 undefined
undefined


// 3. After the declaration statement the variable has value;
(function(){
    console.log(a); // a exists but it is not defined
    var a = 5;
    console.log(a); // a has value
})();

VM82:3 undefined
VM82:5 5
undefined