Undefined array element

Question

I get an " Uncaught TypeError: Cannot read property 'length' of undefined " at line 26. I can't see the reason this is happening, because the console logs line 24 as an array with a value at index 1, but line 25 logs as undefined.

"use strict"
function findpath(G,si,di){
 //G is an array of nodes (with id, lat, lon)
 var P=[si];
 var C=[0,P];
 var M=[C];
 var O=[];
 var ctr=0;
 var done = false;
 var reached = false;
 var best = undefined;
 while(!done){
 ctr++;
 if( ctr > 100 ){
 alert("Sorry, can't find the destination.");
 return P;
 }
 for (var i=0;i<M.length;++i){
 console.log(P);
 console.log(C);
 console.log(M[i]);
 console.log(M[i[0]]);
 var last = M[i[1]].length;
 var v = M[i[1[last]]];
 //select a random neighbor...
 if( v.N.length === 0 ){
 alert("Wat?");
 return [];
 }
 else if( v.N.length === 1 ){
 break;
 }
 else if( v === di ){
 break;
 }
 else {
 for (var j=0;j<v.N.length;++j){
 var temp = M[i];
 O.push(temp[1].push(v.N[j]));
 var dist = distance(v.lat,v.lon,v.N[j].lat,v.N[j].lon);
 var temp2 = O.length-1;
 O[temp2[0]]+=dist;
 if (v.N[j]===di){
 reached = true;
 if (best === undefined){
 console.log("ASSIGN");
 best = O[temp2];
 }
 else {
 if (O[temp2[0]]<best[0]) {
 best = O[temp2];
 }
 }
 }
 }
 }
 }
 M = O;
 var any = false;
 for (var i=0;i<M.length;++i) {
 if (M[i[0]]<best[0]) {
 any = true;
 }
 }
 if (!any) {
 done = true;
 }
 }
 //return the path
 return best[1];
}
function distance(x1,y1,x2,y2){
 return Math.sqrt(Math.pow((x2-x1),2)+Math.pow((y2-y1),2));
}

Output:

Array[1] findpath.js:22
Array[2] findpath.js:23
Array[2]
 0: 0
 1: Array[1]
 0: 13
 length: 1
 __proto__: Array[0]
 length: 2
 __proto__: Array[0] findpath.js:24
undefined findpath.js:25
Uncaught TypeError: Cannot read property 'length' of undefined findpath.js:26

• Musa: What are you trying to do with M[i[0]] and M[i[1[last]]]?

Answer 1

EDIT - per your comments, it looks like you have an array of arrays, and that, if I understand you correctly, M[i[1]] should be M[i][1]

---

You're checking

console.log(M[i[0]]);

but then accessing

 var last = M[i[1]].length;

it seems as though M[i[0]] contains a valid array, but M[i[1]] does not.

I would recommend taking a closer look at your M, and i arrays to figure out why M[i[1]] is undefined.

---

Edit, as the comment below says, i appears to be the loop control variable. Did you mean to type simply M[i] ?

• Musa: i is the loop counter not an array
• iwhitt567: The problem is that console.log(M[i]); returns the contents as 0 in the 0 index, and an array in the 1 index, but both M[i[0]] and M[i[0]] come back as undefined.
• Adam Rackis: @iwhitt567 - if i is an integer, then M[i[0]] is simply invalid. What are you trying to do?
• iwhitt567: In total, M is an array of arrays, and each of those arrays contain an integer as well as another array. Array[Array[0,Array[]]]
• iwhitt567: What I'm trying to do is access the i'th array within M, and then the contents in that inner array.