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    // [1] no value assigned to a, so undefined
    
let a;
 

console.log(a);

// [2] this variable has not been declared and therefore is not defined

// outputs undefined because it is assigned!

console.log(b = undefined);

// [3] so if we compare them yes it's true

console.log(a === b);

// [4] a is not equal to c because it doesn't exist. type prevents error

console.log(a === (typeof c) );

// [5] c is asigned nothing, it will throw an error,

// because it is not declared

console.log(c);

JS difference between not defined and undefined