For inside for get undefined

Question

I have this JSON data:

var lists = [{
 "listId": 1,
 "permission": "WRITE"
 }, {
 "listId": 2,
 "permission": "WRITE"
 }, {
 "listId": 2,
 "permission": "READ"
 }, {
 "listId": 3,
 "permission": "READ"
 }, {
 "listId": 3,
 "permission": "WRITE"
 }, {
 "listId": 5,
 "permission": "WRITE"
 }]

And this one:

var arr = [{
 "listId": 1,
 "confidentiality": "PUBLIC",
 "listName": "List name here..1",
 "permission": "WRITE"
}, {
 "listId": 2,
 "confidentiality": "PUBLIC",
 "listName": "List name here..2",
 "permission": "READ"
}, {
 "listId": 3,
 "confidentiality": "CONFIDENTIAL",
 "listName": "List name here..3",
 "permission": "WRITE"
}, {
 "listId": 4,
 "confidentiality": "CONFIDENTIAL",
 "listName": "List name here..4",
 "permission": "WRITE"
}, {
 "listId": 5,
 "confidentiality": "CONFIDENTIAL",
 "listName": "List name here..5",
 "permission": "WRITE"
}]

And with this for and nested for I must filter data from arr and push it to results[] if is match listId and permission in lists[...]

var result = [];
for(var i = 0; i < arr.length; i++) { 
 for(var j = 0; j < lists.length; j++) { 
 if( (arr[j].listId == lists[i].listId) && (arr[j].permission == lists[i].permission) ) {
 result.push(arr[j]);
 }
 }
}
console.log(result);

The problems is I get listId undefined if arr.length is smaller than lists.length

Any idea how can I solve this?

Answer 1

The problems is I get listId undefined if arr.length is smaller then lists.length

You need to use the respective indexes for their own arrays, i.e. i for arr and j for lists

if( (arr[i].listId == lists[j].listId) && (arr[i].permission == lists[j].permission) )

Answer 2

You could change the structure a bit with a look up table for permissions and use only a single loop for the result set.

var lists = [{ listId: 1, permission: "WRITE" }, { listId: 2, permission: "WRITE" }, { listId: 2, permission: "READ" }, { listId: 3, permission: "READ" }, { listId: 3, permission: "WRITE" }, { listId: 5, permission: "WRITE" }],
 array = [{ listId: 1, confidentiality: "PUBLIC", listName: "List name here..1", permission: "WRITE" }, { listId: 2, confidentiality: "PUBLIC", listName: "List name here..2", permission: "READ" }, { listId: 3, confidentiality: "CONFIDENTIAL", listName: "List name here..3", permission: "WRITE" }, { listId: 4, confidentiality: "CONFIDENTIAL", listName: "List name here..4", permission: "WRITE" }, { listId: 5, confidentiality: "CONFIDENTIAL", listName: "List name here..5", permission: "WRITE" }],
 permissions = {},
 result;
lists.forEach(function (p) {
 permissions[p.listId] = permissions[p.listId] || {};
 permissions[p.listId][p.permission] = true;
});
result = array.filter(function (a) {
 return permissions[a.listId] && permissions[a.listId][a.permission];
});
console.log(result);

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• Carnaru Valentin: Yes, nice example!