Learning JavaScript Data Structures and Algorithms - Third Edition

let and const instead of var

Until ES5, we could declare variables in any place in our code, even if we overwrote the variables declaration, as in the following code:

var framework = 'Angular'; 
var framework = 'React'; 
console.log(framework); 

The output of the preceding code is React, as the last variable declared, named framework, was assigned this value. In the previous code, we had two variables with the same name; this is very dangerous and might drive the code to an incorrect output.

Other languages, such as C, Java, and C#, do not allow this behavior. With ES2015, a new keyword was introduced, called let. let is the new var keyword, meaning we can simply substitute the keyword var for let. In the following code, we have an example: ...