The Syntax of Arrow Functions in JavaScript

The general form of arrow functions in JavaScript consists of the parameter list, the fat arrow, and the body block. Here is an example:

    let f = (a, b) => {
        let c = 4;
        return a + b - c;
    };

However, this could be simplified in some cases. First, if the parameter list contains only one parameter, the parentheses can be removed. For example,

    let f = x => {
        let y = 4;
        return x + y;
    };

Of course, if there are no parameters, the parentheses are required:

    let f = () => {
        let y = 4;
        return 2 + y;
    };

Second, if the body block consists only of a return statement, the curly braces and the return keyword can be eliminated. This is by far the simplest version:

    let f = x => x * x;

In this case, if the return value is an object literal, we need to put it in parentheses to avoid confusion with a block:

    let f = aname => ({
        name: aname
    });

Without parentheses, this could lead to confusing cases, because there are now many shortcuts for object literals. For example, the above function could also be written as the following:

    let f = name => ({
        name
    });

Without parentheses, this would be ambiguous.