'Const' is another type of declaration variable in which the value inside the variable will not change. Unlike 'let', it is impossible to re-declare a variable that is declared by the 'const' keyword. If one tries to re-declare a 'const' variable, then it will result in an error. Although I mentioned that 'let' is the most commonly used keyword, it is more encouraging to use 'const' more often in order to reduce the risk of potential errors.
'Var' is visibally similar to 'let' in its usability. Going deep into the two differences however, 'var' is a function scope while 'let' is a block scope. For now, it is said that 'var' is an older version of 'let' and we would use 'let' instead of 'var'