如何检查元素是否存在于数组中？

Question

I have an array with different ID's. This array is populated from query, so number of ID's can be different each time. So I want to check if my eventID exist in that array, if eventID has matching ID in array I want to alert message, if not I want to submit my form. My problem is when eventID does not match any record in array my form does not get submitted. Here is my code:

 function saveSlots(){
                var records = [];
                var eventID = '#eventID#';
                //here is my array
                records.push(55,56,78,90,44); 

                for(var i=0; i< records.length; i++){
                    if(records[i] == eventID){
                        alert('duplicate')
                    }else{
                        //Submit the form
                    }
                }   

            }

For some reason my else never get executed. In my if statement I just need to check if one of the records from array is matching eventID and if does I do not need to check for other ID's in array. If anyone can help with this problem please let me know.

Answer 1

The way your code is written right now, you'll be submitting the form once for every element that doesn't match, since your conditional if-else will be checked for each item in the array.

I would recommend using a variable to flag that a duplicate was found. Then, after your loop finishes check that variable and decide what to do next:

function saveSlots() {
    var records = [];
    var eventID = '#eventID#';
    //here is my array
    records.push(55, 56, 78, 90, 44);

    var foundDuplicate = false;

    for (var i = 0; i < records.length; i++) {
        if (records[i] == eventID) {
            foundDuplicate = true;
        }
    }

    if(foundDuplicate) {
        alert('Duplicate found!');
    } else {
        alert('Submit form!');
    }
}

Alternatively, you could return to break out of the function as soon as you find a duplicate:

function saveSlots() {
    var records = [];
    var eventID = '#eventID#';
    //here is my array
    records.push(55, 56, 78, 90, 44);

    var foundDuplicate = false;

    for (var i = 0; i < records.length; i++) {
        if (records[i] == eventID) {
            alert('Duplicate found!');
            return;
        }
    }

    alert('Submit form!');
}

Answer 2

There are a couple things that could be preventing you.

1. Make sure to confirm your event id. You have a string '#eventID#' which in javascript will be fine it will still evaluate '55' to 55 so you are ok but make sure you look at the number to see if it is correct.

2. Your loop is going to call your submit multiple times because your looping through it. In other words 60 is not in your array so when it is in the for loop looking at the first value of 55 it does not find it so it submits, then when it does not match 56 it submits again. You should put a break; in the submission code to stop the for loop from continuing if you reach submit. These multiple submits might be causing issues. Even better use index of to look it up. indexOf will return -1 if it is not found so

   function saveSlots(){ var records = []; var eventID = '60'; records.push(55,56,78,90,44); if(records.indexOf(eventID) === -1) { console.log("submission reached"); } }

3. You should confirm that your submission is working properly, you may find that the console.log is being executed, which means the javascript is reaching the correct area but the submission does not seem to work, in this case you know the javascript is fine but there is an issue with your submission.