Get the Index of the Object Inside an Array, Matching a Condition

Get the index of the object inside an array, matching a condition

As of 2016, you're supposed to use Array.findIndex (an ES2015/ES6 standard) for this:

a = [  {prop1:"abc",prop2:"qwe"},  {prop1:"bnmb",prop2:"yutu"},  {prop1:"zxvz",prop2:"qwrq"}];    index = a.findIndex(x => x.prop2 ==="yutu");
console.log(index);

Get the index of the array when array object matching condition

You need recursion

const findItemNested = (arr, level, nestingKey) => (
  arr.reduce((a, item, index) => {
    if (a) return a;
    if (item.level === level) return index;
    if (item[nestingKey]) return findItemNested(item[nestingKey], level, nestingKey)
  }, null)
);
const testArr = [
      {
        'id':'id_1',
       'level':'1-1',
       'children':[
         {'id':'id_1'},
         {'level':'1-1-0'},
         {'children':[]}
       ]
      },
      {'id':'id_2','level':'2-2','children':[{'id':'id_1'},{'level':'2-1-0'},{'children':[]}]}
  ];

const res = findItemNested(testArr, '2-1-0', "children");

console.log(res) //  1

How can I get the index of an object by its property in JavaScript?

As the other answers suggest, looping through the array is probably the best way. But I would put it in its own function, and make it a little more abstract:

function findWithAttr(array, attr, value) {
    for(var i = 0; i < array.length; i += 1) {
        if(array[i][attr] === value) {
            return i;
        }
    }
    return -1;
}

var Data = [
    {id_list: 2, name: 'John', token: '123123'},
    {id_list: 1, name: 'Nick', token: '312312'}
];

With this, not only can you find which one contains 'John', but you can find which contains the token '312312':

findWithAttr(Data, 'name', 'John'); // returns 0
findWithAttr(Data, 'token', '312312'); // returns 1
findWithAttr(Data, 'id_list', '10'); // returns -1

The function returns -1 when not found, so it follows the same construct as Array.prototype.indexOf().

Find all index based on condition

The findIndex method returns the index of the first element in the
array that satisfies the provided testing function. Otherwise, it
returns -1, indicating that no element passed the test. - MDN

You can use reduce here:

const a = [
  { prop1: "abc", prop2: "yutu" },
  { prop1: "bnmb", prop2: "yutu" },
  { prop1: "zxvz", prop2: "qwrq" },
];

const result = a.reduce((acc, curr, i) => {
  if (curr.prop2 === "yutu") acc.push(i);
  return acc;
}, []);

console.log(result);

In an array of objects, fastest way to find the index of an object whose attributes match a search

Maybe you would like to use higher-order functions such as "map".
Assuming you want search by 'field' attribute:

var elementPos = array.map(function(x) {return x.id; }).indexOf(idYourAreLookingFor);
var objectFound = array[elementPos];

How to find index of an object by key and value in an javascript array

The Functional Approach

All the cool kids are doing functional programming (hello React users) these days so I thought I would give the functional solution. In my view it's actually a lot nicer than the imperatival for and each loops that have been proposed thus far and with ES6 syntax it is quite elegant.

Update

There's now a great way of doing this called findIndex which takes a function that return true/false based on whether the array element matches (as always, check for browser compatibility though).

var index = peoples.findIndex(function(person) {
  return person.attr1 == "john"
});

With ES6 syntax you get to write this:

var index = peoples.findIndex(p => p.attr1 == "john");

---

The (Old) Functional Approach

TL;DR

If you're looking for index where peoples[index].attr1 == "john" use:

var index = peoples.map(function(o) { return o.attr1; }).indexOf("john");

Explanation

Step 1

Use .map() to get an array of values given a particular key:

var values = object_array.map(function(o) { return o.your_key; });

The line above takes you from here:

var peoples = [
  { "attr1": "bob", "attr2": "pizza" },
  { "attr1": "john", "attr2": "sushi" },
  { "attr1": "larry", "attr2": "hummus" }
];

To here:

var values = [ "bob", "john", "larry" ];

Step 2

Now we just use .indexOf() to find the index of the key we want (which is, of course, also the index of the object we're looking for):

var index = values.indexOf(your_value);

Solution

We combine all of the above:

var index = peoples.map(function(o) { return o.attr1; }).indexOf("john");

Or, if you prefer ES6 syntax:

var index = peoples.map((o) => o.attr1).indexOf("john");

---

Demo:

var peoples = [
  { "attr1": "bob", "attr2": "pizza" },
  { "attr1": "john", "attr2": "sushi" },
  { "attr1": "larry", "attr2": "hummus" }
];

var index = peoples.map(function(o) { return o.attr1; }).indexOf("john");
console.log("index of 'john': " + index);

var index = peoples.map((o) => o.attr1).indexOf("larry");
console.log("index of 'larry': " + index);

var index = peoples.map(function(o) { return o.attr1; }).indexOf("fred");
console.log("index of 'fred': " + index);

var index = peoples.map((o) => o.attr2).indexOf("pizza");
console.log("index of 'pizza' in 'attr2': " + index);

Get index of Object inside Array and use it in a function

Do it in two steps. First create the array of objects, then fill in the comments property by calling the function on each element.

const foo = [
  {
    id: 1,
  },
  {
    id: 34,
  },
  {
    id: 21,
  }
]

foo.forEach(el => el.comments = getComments(el));

function getComments(obj) {
  return obj.id;
}

console.log(foo);

Find index of javascript array of objects based on object field value

You'd have to iterate, here's a very simple example

var index = null;

for (var i=0; i<array.length; i++) {
    if ( array[i].id == 15 ) {
        index = i;
        break;
    }
}

That gets you the index, if you just want to return the object you can do

var obj = array.filter(function(obj) {
    return obj.id == 15;
}).shift();

---

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