javascript数组比较多次循环

Question

so I've retrieved an object containing photos from facebook, Which all works perfectly fine.

for (var i = 0; i < photoLikes.data.length; i++) {

            if (photoLikes.data[i].name === facebook.username) {
                alert("You have already liked this photo. Unliked");
                var count = photoLikes.data.length;
                //facebook.unlikePhoto(id, count);
            }

^^ this code works above,

BUT the issue is when seeing if the name ISNT in the array , what it does is it iterates over every item and if it isnt equal to the username (searching if username is in the object) calls the else statement.

I just need it to be called once. anyone have any idea? this is my statement for not in. I've tried this:

for (var x = 0; x < photoLikes.data.length; x++) {

    if (facebook.photos.indexOf(facebook.username == -1)) {

        console.log("increment");
    }
}

and

for (var x = 0; x < photoLikes.data.length; x++) {

    if (photoLikes.data[i].name != facebook.username) {

        console.log("increment");
    }
}

and both trigger every time.

Thanks

edit: I'm trying to break out of the for loop once the if condition is met.

Answer 1

Basically the (very good) answer of user1680977, but improved with some design patterns (single var, optimized for loop, type safe comparison):

var found = false,
    i, count;

for (i = 0, count = photoLikes.data.length; i < count; i++) {
    if (photoLikes.data[i].name === facebook.username) {
        found = true;
        break;
    }
}

if (found === false) {
    alert("The name was not found in the array");
}

Don´t use "else" in the loop if you don´t need it, keep code in loops as small and fast as possible.

indexOf will not work, because the name is not the key. There is a nice filter method, but not worth it in that case. You may also check out the answer in this thread for more solutions: How do I check if an array includes an object in JavaScript?

Btw, this would be perfect as function, no break needed:

function isUserInArray(likeArray, username) {
    var i, count;

    for (i = 0, count = likeArray.length; i < count; i++) {
        if (likeArray[i].name === username) {
            return true;
        }
    }
    return false;
}

Answer 2

I'm not exactly sure I know what you're trying to accomplish.

If you're attempting to break out of the for-loop you can simply use the break command. If you are trying to execute a piece of code once in all of the iterations of your for loop you could do something like this.

var executedElse = false;
for( ...... ){
    if( some-condition ){
        // do work
    } else {
        if( !executedElse ){
            // do work
            executedElse = true;
        }
    }
}

Answer 3

Perhaps try it like this

var found = false;
for (var i = 0; i < photoLikes.data.length; i++) {

    if (photoLikes.data[i].name == facebook.username) {
        found = true;
        break;
    }
}

if (found === false) {
    alert("The name was not found in the array");
}

Answer 4

Use the break statement:

for (var x = 0; x < photoLikes.data.length; x++) {

    if (facebook.photos.indexOf(facebook.username == -1)) {

        console.log("increment");
        break;
    }
}

MDN docs

Also your if condition is wrong. It should be:

if (facebook.photos.indexOf(facebook.username) == -1) {
    ...
}