JavaScript arrow functions are unnamed functions which are best used as non-method functions. They provide a short hand notation for using functions. An arrow function consists of a list of function parameters followed by an arrow which is followed by an expression to be returned or a code block. The following code shows how to create an arrow function
let ToUpperWrapper = (value) => {value.toUpperCase();}
ToUpperWrapper("test");The let keyword is used to define a variable with a local scope. A variable declared using let can only be used in the block, expression or statement in which it is used as well as in sub blocks. The var keyword allows a variable to be used globally or within a function block. Variables created with var can be accessed any where within the enclosing function
See the article Arrow functions for more information about using JavaScript arrow functions