三元运算符如何调用函数？

Question

Given following code:

 const letters = ['a', 'b', 'c']; foo = ((list, letter) => { if (list.includes(letter)) { return true; } return false; })(letters, 'c') ? 'letter in list' : 'letter not in list'; console.log(foo);

Output will be:

letter in list

How does ternary operator work in this example? Does it call foo with letters and c as parameters? How does it know to call this function?

Answer 1

You can split up the expression in several parts, and look at them individually:

foo = (
    (
        // Create an arrow function
        (list, letter) => {
            if (list.includes(letter)) {
                return true;
            }
            return false;
        }
    )
    // call the function
    (letters, 'c')
) /* ternary operator on call result */ ? 'letter in list' : 'letter not in list';

If you're unsure, you can usually replace expressions with variables to make it more clear:

const func = (list, letter) => {
    if (list.includes(letter)) {
        return true;
    }
    return false;
};
const callResult = func(letters, 'c');
const foo = callResult ? 'letter in list' : 'letter not in list';

Most people would even say it should've used several variables anyway for readability.