Maximum number of values in an array

I have an array to have a maximum of 10 elements. Whenever I add a new element, if it already has 10, it would remove the first and push a new one.

I made this:

Array.prototype.pushMax = function(value,max){

     if (this.length >= max){
           this.shift();
     }
     this.push(value);

}

Which seems to work fine, however, I'm just wondering if there is a better way to do it (perhaps some native JavaScript function)

There is no native way to do this so your general logic seems sound. Here's some improvements, you might consider:

-
Make sure the pushMax function is not enumerable so people who iterate arrays with for (var index in array) won't see the pushMax property.

-
Ensure the array stays below max length even if it was previously above max

-
Return the new length of the array, the same as .push():

Here's a working snippet:



Object.defineProperty(Array.prototype, "pushMax", {
configurable: false,
enumerable: false,
writable: false,
value: function(value, max) {
if (this.length >= max) {
this.splice(0, this.length - max + 1);
}
return this.push(value);
}
});

var x = [0,1,2,3,4,5,6,7,8,9,10];
x.pushMax(11, 10);
x.pushMax(12, 10);
x.pushMax(13, 10);

// wrong way to iterate an array, but just testing enumerability
for (var i in x) {
document.write(i + ": " + x[i] + "
");
}



You could also consider making the max length be a non-enumerable property of the array so you don't have to pass it to .pushMax() every time.

I'd really rather see this in a subclass of an Array rather than modifying the built-in Array object, but alas we can't subclass the Array object yet in most browsers.

StackExchange Code Review Q#101235, answer score: 3