在遍历数组时遇到JavaScript错误

Question

function sortproducts(filprodlist)
{
    var prod;
    var k = 0;
    for (i = 0; i < filprodlist.length; i++) {
        var k = i + 1;
        var p=filprodlist[i].EntityKey.substr(filprodlist[i].EntityKey.length - 1);
        var p2=filprodlist[k].EntityKey.substr(filprodlist[k].EntityKey.length - 1);
        if ( p>p2)  {
            temp = filprodlist[k];
            filprodlist[k] = filprodlist[i];
            filprodlist[i] = temp;
        }
    }
    rederProduct(filprodlist);
}

while executing above code getting following error TypeError: filprodlist[k] is undefined

Answer 1

Reason

On last iteration, when i is at last element of array. You are fetching are using var k = i + 1; , where k doesn't exists. Thus you are getting the error.

So Use

for (i = 0; i < filprodlist.length - 1; i++) {

instead of

for (i = 0; i < filprodlist.length; i++) {

Answer 2

Let's say filprodlist has 10 items. Then the items are indexed 0-9 and Your i goes through 0-9. In every iteration You define k = i + 1 . So in the last iteration i = 9 , k = 10 and You are trying to access filprodlist[10] which doesn't exist (returns undefined ). Solution is in @Satpal's answer.

Answer 3

Don't var inside loops, blocks don't have scope in JavaScript , var every variable you want to use in one var statement. End your loop when the highest index reaches the end ( k ). You can move k into the for 's iterate step because you're really iterating with this, too.

function sortproducts(filprodlist) {
    var prod, i, k, p, p2, temp;
    for (i = 0, k = 1; k < filprodlist.length; ++i, ++k) {
        p =  filprodlist[i].EntityKey.substr(filprodlist[i].EntityKey.length - 1);
        p2 = filprodlist[k].EntityKey.substr(filprodlist[k].EntityKey.length - 1);
        if (p > p2)  {
            temp = filprodlist[k];
            filprodlist[k] = filprodlist[i];
            filprodlist[i] = temp;
        }
    }
    rederProduct(filprodlist);
}

A different way to do it is forget k all together, start from i = 1 and use i - 1 and i , this means you're iterating with less variables so it might be easier for you to follow the code in your mind.