从JavaScript中的数组中删除项目

Question

Seen this question a lot, but cannot find something that's what i'm looking for.

onClick I push an item to an array I have, however, if there's 3 items in my array I don't want to be able to push items anymore.

var selectedData = [];

I set my empty variable.

var index = selectedData.indexOf(3);

I then get the index of my array which is 3

if (index > 3) {
  selectedData.splice(index, 1);
}

Then within my if statement I say, if my index which is 3, is bigger then 3, then splice at index and remove one.

selectedData.push(TheThing);

I then push TheThing to my array if the if statement above isn't true.

However, I have a variable var arrayLength = selectedData.length; that grabs the length, and when I console log it, it starts at 0 and splices items anything after 4. Not 3.

Any idea what i've done wrong or misunderstood? Thanks

---

More full example of my code

var selectedData = [];

myElement.on('click', function() {

  var index = selectedData.indexOf(3);
      if (index > 3) {
          selectedData.splice(index, 1);
      }
  var arrayLength = selectedData.length;

  console.log(arrayLength, 'the length');

});

So in short, onClick check my array and remove anything after the third that gets added into my array.

Answer 1

Do you want this to behave as a stack or a queue?

So your code here:

var index = selectedData.indexOf(3);

Is not grabbing the 3rd index - its grabbing the first index where it sees 3, or -1 if it doesn't. Replace your if statement with,

if (selectedData.length > 3) {
    selectedData.pop() // removes last element (stack)
    // or
    selectedData = selectedData.slice(1) //remove first element (queue)
}

Answer 2

I think you need to try var arrayLength = selectedData.length -1;

You start at 0 like a normal array, but don't you start with an empty array?

Plus when you use .length , it returns the true count of the array or collection not a 0 index. `

Answer 3

you can override push() method of your array like this:

var a = [];
a.push = function(){}

or like this

a.push = function (newEl){
  if(this.length <3){
    Array.prototype.push.call(this, newEl)
  }
}

This is not complete example because push() can take many arguments and you should to handle this case too

Answer 4

var index = selectedData.indexOf(3); simply give you the index of the element of the array that has value 3 Example

 selectedData = [ 0, 3 , 2];
 alert( selectedData.indexOf( 3 ) ); // this will alert "1" that is the index of the element with value "3"

Answer 5

you can use this scenario

var selectedData = [];

myElement.on('click', function() {

  //if selectedData length is less than 3, push items

});

Answer 6

This could work.

myElement.on('click', function() {

    if(selectedData.length > 3){
        selectedData = selectedData.splice(0, 3);
    }

    console.log(selectedData.length, 'the length');

});