Determining the position of an item within an array by examining its attributes

Question

Determining the position of an item within an array by examining its attributes

Recently, I encountered a dilemma with a JavaScript array containing objects structured like such:

var myArray = [{...}, {...}, {...}];

Within each object lies a unique id, along with other properties:

{ 
  id: 4,
  property1: 'something',
  property2: 'something'
}

The burning question is how exactly can one determine the index of a specific object in this array solely based on its id? For instance, if we are aware that myArray[x].id == 4, what steps should be taken to find out the exact value of x?

javascript arrays object

Answer 1

Answer №1

let idx = myItems.map((item) => {
  return item.num;
}).indexOf(4);

If you're working with Internet Explorer versions older than 9, you may need to apply a workaround for the map method or resort to using a traditional loop.

Answer 2

let idx = myItems.map((item) => {
  return item.num;
}).indexOf(4);

If you're working with Internet Explorer versions older than 9, you may need to apply a workaround for the map method or resort to using a traditional loop.

Answer 3

Answer №2

Alternatively, using ES6 syntax:

const position = myArray.map( element => element.id ).indexOf(42)

or

const position = myArray.findIndex( element => element.id === 42 )

Answer 4

Alternatively, using ES6 syntax:

const position = myArray.map( element => element.id ).indexOf(42)

or

const position = myArray.findIndex( element => element.id === 42 )

Answer 5

Answer №3

Why not consider implementing a loop instead?

function findIndexById(arr, identifier) {
    for (let index = 0; index < arr.length; index++) {
       if (arr[index].id === identifier) return index;
    }
    return -1;
}

Just because there are various features available in JavaScript or its libraries doesn't mean you should always rely on them without utilizing a simple loop when necessary. Sometimes, simplicity and efficiency matter the most.

Answer 6

Why not consider implementing a loop instead?

function findIndexById(arr, identifier) {
    for (let index = 0; index < arr.length; index++) {
       if (arr[index].id === identifier) return index;
    }
    return -1;
}

Just because there are various features available in JavaScript or its libraries doesn't mean you should always rely on them without utilizing a simple loop when necessary. Sometimes, simplicity and efficiency matter the most.

Answer 7

Answer №4

Check out ES6 Array.findIndex method

const newArray = [{id:1}, {id:2}, {id:3}];
const indexFound = newArray.findIndex((element) => (element.id === 3));

Answer 8

Check out ES6 Array.findIndex method

const newArray = [{id:1}, {id:2}, {id:3}];
const indexFound = newArray.findIndex((element) => (element.id === 3));

Answer 9

Answer №5

When ensuring each ID is distinct, the following approach can be taken:

obj1 = {id:101}
obj2 = {id:202}
obj3 = {id:303}
obj4 = {id:404}
arr = [obj1,obj2,obj3,obj4]
arr.indexOf( arr.filter( function(item){return item.id==404} )[0] );

Answer 10

When ensuring each ID is distinct, the following approach can be taken:

obj1 = {id:101}
obj2 = {id:202}
obj3 = {id:303}
obj4 = {id:404}
arr = [obj1,obj2,obj3,obj4]
arr.indexOf( arr.filter( function(item){return item.id==404} )[0] );

Answer 11

Answer №6

One alternative approach is to consider using a recursive function, although the solution provided by @xdazz is quite appealing.

function findIndexById(array, targetId, currentIndex) {
    if (!currentIndex) { currentIndex = 0; }
    if (array[currentIndex].id === targetId) {
        return currentIndex;
    }
    return ((currentIndex += 1) >= array.length) ? -1 : findIndexById(array, targetId, currentIndex);
};

Answer 12

One alternative approach is to consider using a recursive function, although the solution provided by @xdazz is quite appealing.

function findIndexById(array, targetId, currentIndex) {
    if (!currentIndex) { currentIndex = 0; }
    if (array[currentIndex].id === targetId) {
        return currentIndex;
    }
    return ((currentIndex += 1) >= array.length) ? -1 : findIndexById(array, targetId, currentIndex);
};

Answer 13

Answer №7

One useful method to consider is .reduce(), which enables you to condense an Array into a single value.

var obj_idx = myArray.reduce(function(idx, item, i) {
  return item.id === 4 ? i : idx;
}, -1);

In case no match is found, the default value of -1 is returned.

If you find yourself needing this functionality in multiple instances, creating a function factory might be a good idea.

function idxForID(target) {
    return function(idx, item, i) {
      return item.id === target ? i : idx;
    };
}

This can then be implemented as shown below.

var obj_idx = myArray.reduce(idxForID(4), -1);

Answer 14

One useful method to consider is .reduce(), which enables you to condense an Array into a single value.

var obj_idx = myArray.reduce(function(idx, item, i) {
  return item.id === 4 ? i : idx;
}, -1);

In case no match is found, the default value of -1 is returned.

If you find yourself needing this functionality in multiple instances, creating a function factory might be a good idea.

function idxForID(target) {
    return function(idx, item, i) {
      return item.id === target ? i : idx;
    };
}

This can then be implemented as shown below.

var obj_idx = myArray.reduce(idxForID(4), -1);

Determining the position of an item within an array by examining its attributes

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

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