React Express

Fat Arrow Functions
Fat Arrow Functions
The fat arrow => is used to define anonymous functions. There are two important differences in the behavior of these functions, compared to functions defined with function.
First, the binding for the keyword this is the same outside and inside the fat arrow function. This is different than functions declared with function, which can bind this to another object upon invocation. Maintaining the this binding is very convenient for operations like mapping: => this.doSomethingWith(x)).
Second, fat arrow functions don't have an arguments object defined. You can achieve the same thing using the spread syntax: (...args) => doSomething(args[0], args[1]).
The fat arrow function syntax can vary a bit. If the function takes exactly one parameter, the parentheses can be omitted: x => Math.pow(x, 2). Any other number of arguments will need parentheses: (x, y) => Math.pow(x, y). If the function body is not wrapped in curly braces (as in the previous sentences), it is executed as an expression, and the return value of the function is the value of the expression. The function body can be wrapped in curly braces to make it a block, in which case you will need to explicitly return a value, if you want something returned. You will likely use the curly braces and block version more frequently, as this allows the function body to include multiple lines of code.