“Quelle est la différence entre non définie, non déclarée, nul” Réponses codées

Quelle est la différence entre non définie, non déclarée, nul

What is the Difference between Undefined, undeclared, Null

// undefined means that the variable has not been declared, or has not been given a value.
// Undefined is used for unintentionally missing values.
var dog;
console.log(dog);


// Undeclared means the variable does not exist in the program at all.
console.log(cat);


// Null used for intentionally missing values. It contains no value.