Can I limit the length of an array in JavaScript

Question

I want to display the product browsing history  so I am storing the product ids in a browser cookie   Because the list of history is limited to 5 items  I convert the cookie value to an array  then check the length of it and cut the redundant    The code below is what I have tried  but it does not work  the array item isn t removed   I would like to ask how to limit the array length so it can only store 5 items   Or  How can I cut the items after the array index 4   var id   product id  var browseHistory     cookie  history    if  browseHistory    null      var old cookie     cookie  history      var new cookie          if  old cookie indexOf         -1        var arr   old cookie split           if  arr length  gt   5          arr splice 4  1               new cookie   id         old cookie      cookie  history   new cookie    expires  7  path            else       cookie  history   id    expires  7  path

User · Answer

The fastest and simplest way is by setting the .length property to the desired length:

arr.length = 4;

This is also the desired way to reset/empty arrays:

arr.length = 0;

Caveat: setting this property can also make the array longer than it is: If its length is 2, running arr.length = 4 will add two undefined items to it. Perhaps add a condition:

if (arr.length > 4) arr.length = 4;

Alternatively:

arr.length = Math.min(arr.length, 4);

User · Answer

var  arrLength   arr length  if arrLength  gt  maxNumber       arr splice  0  arrLength - maxNumber       This soultion works better in an dynamic environment like p5js  I put this inside the draw call and it clamps the length of the array dynamically    The problem with    arr slice 0 5       is that it only takes a fixed number of items off the array per draw frame  which won t be able to keep the array size constant if your user can add multiple items   The problem with   if  arr length  gt  4  arr length   4       is that it takes items off the end of the array  so which won t cycle through the array if you are also adding to the end with push

User · Answer

You need to actually use the shortened array after you remove items from it   You are ignoring the shortened array   You convert the cookie into an array   You reduce the length of the array and then you never use that shortened array   Instead  you just use the old cookie  the unshortened one      You should convert the shortened array back to a string with  join      and then use it for the new cookie instead of using old cookie which is not shortened   You may also not be using  splice   correctly  but I don t know exactly what your objective is for shortening the array   You can read about the exact function of  splice   here

User · Answer

You re not using splice correctly   arr splice 4  1    this will remove 1 item at index 4  see here  I think you want to use slice   arr slice 0 5    this will return elements in position 0 through 4    This assumes all the rest of your code  cookies etc  works correctly

User · Answer

I think you could just do   let array       array length   2  Object defineProperty array   length    writable false      array 0    1     1  undefined   array 1    2     1  2   array 2    3     1  2  - gt  doesn t add anything and fails silently  array push  something      but this throws an Uncaught TypeError

User · Answer

arr length   Math min arr length  5

[javascript] Can I limit the length of an array in JavaScript?

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