未捕获的TypeError：无法读取未定义的属性“ 1”

Question

I'm working on an inventory function, however, I keep getting error: Uncaught TypeError: Cannot read property '1' of undefined. I don't think I'm going over the length of array, so why am I getting "property '1' undefined". Obviously I"m trying to read something is not there. I just can't see it. Any help appreciated. I used the console.log to try to log the error. but everything comes back with an output. Thanks

 function updateInventory(arr1, arr2) { // All inventory must be accounted for or you're fired! for(var i = 0; i < arr1.length; i++) { //if item found, update var index = findItem(arr1[i][1], arr2); if(index != undefined) { arr1[i][0] += arr2[i][0]; } else { arr1.push(arr2[index]); } } //sort arr1 arr1.sort(function(first, second) { return (first[1] > second[1]) ? 1 : -1; }); return arr1; } //helper method to search arr2 function findItem(item, arr2) { for(var i = 0; i < arr2.length; i++) { if(item === arr2[i][1]) return i; } return undefined; } // Example inventory lists var curInv = [ [21, "Bowling Ball"], [2, "Dirty Sock"], [1, "Hair Pin"], [5, "Microphone"] ]; var newInv = [ [2, "Hair Pin"], [3, "Half-Eaten Apple"], [67, "Bowling Ball"], [7, "Toothpaste"] ]; updateInventory(curInv, newInv); 

Answer 1

in the code else { arr1.push(arr2[index]); } else { arr1.push(arr2[index]); } index will be undefined here. which will result in undefined getting pushed into arr1, and you are running loop over same array. so var index = findItem(arr1[i][1], arr2) will give the error you see. It will be better if you update the other array with updated values.

 function updateInventory(arr1, arr2) { // All inventory must be accounted for or you're fired! for(var i = 0; i < arr1.length; i++) { //if item found, update var index = findItem(arr1[i][1], arr2); if(index != undefined) { arr2[index][0] += arr1[i][0]; }else{ arr2.push(arr1[i]); } } //sort arr2 arr2.sort(function(first, second) { return (first[1] > second[1]) ? 1 : -1; }); return arr2; } //helper method to search arr2 function findItem(item, arr2) { for(var i = 0; i < arr2.length; i++) { if(item === arr2[i][1]) return i; } return undefined; } // Example inventory lists var curInv = [ [21, "Bowling Ball"], [2, "Dirty Sock"], [1, "Hair Pin"], [5, "Microphone"] ]; var newInv = [ [2, "Hair Pin"], [3, "Half-Eaten Apple"], [67, "Bowling Ball"], [7, "Toothpaste"] ]; console.log(updateInventory(curInv, newInv));