JavaScript insert into Array at index

Question

I know how to insert into array at index, when that index is already present. Say arr = [1, 2, 3, 4] and arr.splice(2, 0, 0) will result in [1, 2, 0, 3, 4]. However I have an empty array which is getting filled from an object which is not in any particular order. Actually array is used to sort the object:

var key = parseInt(object[object_key].timestamp);
while (key && array_sorted[key]) { //Attempt at preventing overwriting elements with same timestamp
 key++;
}
key = key ? key : array_sorted.length + 1;
array_sorted.splice(key, 0, object[object_key].data);

Now this will build an array [object[0].timestamp, object[1].timestamp, object[2].timestamp, ...] instead of something like this [undefined, ..., undefined, object[4].timestamp, object[3].timestamp, undefined, object[0].timestamp, undefined, ..., undefined, object[1].timestamp]... How can I achieve sorting of an object of objects by timestamp (object's object's property) using this method? Is there a way to insert at index of an empty array?

• megawac: var a = []; a.splice(2, 0, 'test'); works if you want to insert at the start of the array or index 2. Otherwise wouldn't a[2] = 'test' work for you
• Xeos: @megawac a.length returns 1 instead of 3 a[2] will create object with empty array and element with key "2"...
• shennan: Are trying to index these with the timestamp as a key? Because your array_sorted.length property (fed to the key when the key doesn't validate) could override potential keys...
• Xeos: @shennan console.log(key) before .splice() and it returns correct key. When I .log(array_sorted) I get regular array without any "undefined" instances...
• webduvet: I' afraid JS doesn't have array like PHP.

Answer 1

To answer the actual question, Objects in Javascript do not guarantee any order.

To get the kind of order-based behaviour that you want out of your object of objects, you really need to convert it into an array of objects. You can then sort it with the sort method as per Anand's suggestion.

Or you could sort them as you go:

var objects = {
 1:{timestamp:"12345"},
 2:{timestamp:"34567"},
 3:{timestamp:"23456"}
}
var array = [];
for(var i in objects){
 var timestamp = parseInt(objects[i].timestamp);
 var added = false;
 for(var j in array){
 if(timestamp > parseInt(array[j].timestamp)){
 array.splice(j + 1, 0, objects[i]);
 added = true;
 break;
 }
 }
 if (!added) {
 array.unshift(objects[i]);
 }
}

• Xeos: Exactly! Thanks. I've added a check added, that will make sure that if all of the keys are bigger than the one to get added, it will still be inserted.
• shennan: @Xeos as you were adding that edit I was also noticing the bug and writing it up. I even used the same added variable name :-). Have edited further as we no longer need the check on the variable length. If the item hasn't been added, that will catch it. Also, using unshift feels more elegant.

Answer 2

I am not going specific but the given example below could help you to solve your problem.

lets say we have

var objArray=[{"Name":"Anand"},{"Name":"Jhon"},{"Name":"Paul"}];

now you can sort like

objArray.sort(function(a, b) {
 var textA = a.Name.toUpperCase();
 var textB = b.Name.toUpperCase():;
 return (textA < textB) ? 1 : (textA > textB) ? -1 : 0;
 //return (textA < textB) ? -1 : (textA > textB) ? 1 : 0; //for ascending.
 });

now you will find sorted array.

• Anand Jha: I am just explaining some sort of logical approach in common not for the specific problem.

Answer 3

Not sure that I understood correctly your question. Actually there are several question's as I can see and I'll try to answer them:

Sort Object

You can't sort the object, but you can make an array containing object's properties keys or values sorted by some criteria.

var object = {
 a: {
 timestamp: 1385127590866
 },
 c: {
 timestamp: 1385127590872
 },
 b: {
 timestamp: 1385127590877
 }
},
keys = Object.keys(object), // Get object properties as array
sortedByKeys = keys.sort(function(key0, key1) { // ['a', 'b', 'c']
 if(key0 < key1) return -1;
 if(key1 > key0) return 1;
 return 0;
}),
sortedByTimestamp = keys.sort(function(key0, key1) { // ['a', 'c', 'b']
 return object[key1] - object[key0];
}),
sortedValues = [], i, j;
for(i=0, l=sortedByTimestamp.length; i<l; i++) { // [{timestamp:1385127590866}, {timestamp:1385127590872}, {timestamp:1385127590877}]
 sortedValues.push(object[sortedByTimestamp[i]]);
}

Create empty array an place item at specific index

var array = Array(Object.keys().length); // [undefined, undefined, undefined]
array[1] = object['a']; // [undefined, {timestamp:1385127590866}, undefined]

Hope it will help.