index.html

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script>
        
        const variable_constante = 12
        let variable_libre = 34
        variable_libre = 23
        var variable_obsolete = 13
        
        const texte1 = 'toto'
        const texte2 = "titi"
        const texte3 = `tata`
        let texte4 = texte1 + '' + texte2
        texte4 = `${texte2} ${texte3}`

        const isTrue = true

        const nullVar = null

        const tableau = [ 2, 3,'toto', [1, 
        3 ,4]]

        let variable_tabl = tableau[2]

        let obj_perso = {
            nom: "Toto",
            prenom:'titi'
        }
        
        obj_perso.nom = "Tata"
        obj_perso[prenom] = 'Tutu'
        const key = 'prenom'
        obj_perso[key] = 'Arnulf'

        typeof tableau //object

    </script>
</head>
<body>
    
</body>
</html>