Getting the first index of an object

Question

Consider:

var object = {
  foo: {},
  bar: {},
  baz: {}
}

How would I do this:

var first = object[0];
console.log(first);

Obviously, that doesn’t work because the first index is named foo, not 0.

console.log(object['foo']);

works, but I don’t know it’s named foo. It could be named anything. I just want the first.

Answer 1

There is no way to get the first element, seeing as "hashes" (objects) in JavaScript have unordered properties. Your best bet is to store the keys in an array:

var keys = ["foo", "bar", "baz"];

Then use that to get the proper value:

object[keys[0]]

Answer 2

I had the same problem yesterday. I solved it like this:

var obj = {
        foo:{},
        bar:{},
        baz:{}
    },
   first = null,
   key = null;
for (var key in obj) {
    first = obj[key];
    if(typeof(first) !== 'function') {
        break;
    }
}
// first is the first enumerated property, and key it's corresponding key.

Not the most elegant solution, and I am pretty sure that it may yield different results in different browsers (i.e. the specs says that enumeration is not required to enumerate the properties in the same order as they were defined). However, I only had a single property in my object so that was a non-issue. I just needed the first key.

Answer 3

Using underscore you can use _.pairs to get the first object entry as a key value pair as follows:

_.pairs(obj)[0]

Then the key would be available with a further [0] subscript, the value with [1]

Answer 4

Based on CMS answer. I don't get the value directly, instead I take the key at its index and use this to get the value:

Object.keyAt = function(obj, index) {
    var i = 0;
    for (var key in obj) {
        if ((index || 0) === i++) return key;
    }
};


var obj = {
    foo: '1st',
    bar: '2nd',
    baz: '3rd'
};

var key = Object.keyAt(obj, 1);
var val = obj[key];

console.log(key); // => 'bar'
console.log(val); // => '2nd'

Answer 5

Just for fun this works in JS 1.8.5

var obj = {a: 1, b: 2, c: 3};
Object.keys(obj)[0]; // "a"

This matches the same order that you would see doing

for (o in obj) { ... }

Answer 6

To get the first key of your object

const myObject = {
   'foo1': { name: 'myNam1' },
   'foo2': { name: 'myNam2' }
}

const result = Object.keys(myObject)[0];

// result will return 'foo1'