One of the biggest problems with declaring variables with the
var keyword is that you can overwrite variable declarations without an error.
Here the console will display the string
As you can see in the code above, the
camper variable is originally declared as
James and then overridden to be
David. In a small application, you might not run into this type of problem, but when your code becomes larger, you might accidentally overwrite a variable that you did not intend to overwrite. Because this behavior does not throw an error, searching and fixing bugs becomes more difficult.
A new keyword called
let was introduced in ES6 to solve this potential issue with the
var keyword. If you were to replace
let in the variable declarations of the code above, the result would be an error.
This error can be seen in the console of your browser. So unlike
var, when using
let, a variable with the same name can only be declared once. Note the
"use strict". This enables Strict Mode, which catches common coding mistakes and “unsafe” actions. For instance:
let camper = 'James'; let camper = 'David'; "use strict"; x = 3.14;