函数不返回值

Question

I have this function `

let n = (index) => {
    if(index < 0){
        index = 0;  
    }
    return index;}

that must run inside of this function,

prev.addEventListener('click', function() {  
    index--;
    n(index);
    console.log(index);
});

but for some reasons it wouldn't work. It looks like it sets the value of index, but actually it doesn't

Answer 1

You are forgetting to set your index to the value returned by the function.

prev.addEventListener('click', function() {  
    index--;
    index = n(index);
    console.log(index);
});

Answer 2

In here you have called the function n(index) but it's value isn't assigned anywhere, you have to assign it's value like below

let n = (index) => {
    if(index < 0){
        index = 0;  
    }
    return index;}

prev.addEventListener('click', function() {  
    index--;
    index = n(index); // This is where you have Assign it's Value
    console.log(index);
});