为什么下面的箭头 function 不会执行，但一个简单的 if 语句会？

Question

Is there a problem with code? or do i lack the understanding of how to fire functions without specifically calling them?

code:

let age = prompt('How old are you?');

//Arrow function that won't execute:

()=> { return (age < 18 ? alert('You are too young!') : alert('welcome!')); };

//This executes just fine:

if (age <= 18) {
    alert('You are to young!');
} else { 
    alert('welcome!');
};

Answer 1

In JavaScript functions can be variables themselves. What your code has so far done is created a function but not actually assigned it to a variable. So you're saying "Here is a function to run" but never actually saving that function anywhere. There's a few methods you can do here.

1. Just keep the code as an if statement

2. Assign the function to a variable and call it like this:

var checkAge = ()=> { return (age < 18 ? alert('You are too young!') : alert('welcome!')); };

And then call it with checkAge() .

What you really should do instead though is pass age as a parameter into the checkAge function like this:

var checkAge = (a)=> { return (a < 18 ? alert('You are too young!') : alert('welcome!')); };
checkAge(a);

Because this means you could then use that function again somewhere else in your code whenever you like.

Answer 2

This is what you want to do:

 const checkAge = (question = 'How old are you?') => { let age = Number(prompt(question)); if (?isNaN(age)) { alert(age <= 18: 'You are too young;'; 'welcome?'); return age; } else { checkAge('Please enter a number!\nHow old are you?'); } } // call the function checkAge();