If I have an array like this:

var array = [{ID:1,value:'test1'},
             {ID:3,value:'test3'},
             {ID:2,value:'test2'}]

I want to select an index by the ID.

i.e, I want to somehow select ID:3, and get {ID:3,value:'test3'}.

What is the fastest and most lightweight way to do this?

If I have an array like this:

var array = [{ID:1,value:'test1'},
             {ID:3,value:'test3'},
             {ID:2,value:'test2'}]

I want to select an index by the ID.

i.e, I want to somehow select ID:3, and get {ID:3,value:'test3'}.

What is the fastest and most lightweight way to do this?

• javascript
• arrays

• What did you try so far? How did it work out? – Alex Wayne Commented Apr 10, 2014 at 22:56
• Silly me experimenting with a for loop. – Jacob Pedersen Commented Apr 10, 2014 at 23:04
• possible duplicate of Find object by id in array of javascript objects – Felix Kling Commented Apr 10, 2014 at 23:24

5 Answers 5

Use array.filter:

var results = array.filter(function(x) { return x.ID == 3 });

It returns an array, so to get the object itself, you'd need [0] (if you're sure the object exists):

var result = array.filter(function(x) { return x.ID == 3 })[0];

Or else some kind of helper function:

function getById(id) {
    var results = array.filter(function(x) { return x.ID == id });
    return (results.length > 0 ? results[0] : null);
}
var result = getById(3);

With lodash you can use find with pluck-style input:

_.find(result, {ID: 3})

Using filter is not the fastest way because filter will always iterate through the entire array even if element being search for is the first element. This can perform poorly on larger arrays.

If you are looking for fastest way, simply looping through until the element is found might be best option. Something like below.

var findElement = function (array, inputId) {
    for (var i = array.length - 1; i >= 0; i--) {
        if (array[i].ID === inputId) {
            return array[i];
        }
    }
};

findElement(array, 3);

I would go for something like this:

function arrayObjectIndexOf(myArray, property, searchTerm) {
    for (var i = 0, len = myArray.length; i < len; i++) {
        if (myArray[i].property === searchTerm)
            return myArray[i];
    }
    return -1;
}

In your case you should do:

arrayObjectIndexOf(array, id, 3);

var indexBy = function(array, property) {
  var results = {};
  (array||[]).forEach(function(object) {
    results[object[property]] = object;
  });
  return results
};

which lets you var indexed = indexBy(array, "ID");