Question

Array.prototype.move = function(oldIndex, newIndex) {
    var val = this.splice(oldIndex, 1);
    this.splice(newIndex, 0, val[0]);
}

//Testing - Change array position
var testarray = [1, 2, 3, 4];
testarray.move(3, 0);
console.log(testarray);

This produces an error “this.splice is not a function” yet it returns the desired results. Why?

Answer 1

Array.prototype.move = function(oldIndex, newIndex) {
    if(Object.prototype.toString.call(this) === '[object Array]') {
        if(oldIndex && typeof oldIndex == 'number' && newIndex && typeof newIndex == 'number') {
            if(newIndex > this.length) newIndex = this.length;
            this.splice(newIndex, 0, this.splice(oldIndex, 1)[0]);
        }
    }
};

For some reason, the function is being called by the called by the document on load (still haven’t quite figured that one out). I added a few checks to verify that this = an array, and then also reset the new index to be equal to the total size if the supplied int was greater than the total length. This solved the error issue I was having, and to me is the simplest way to move objects around in an array. As for why the function is being called onload must be something to do with my code.