I have an Array, like this one:

let myarr = [
  {type:"a", class:"x", value:"p"},
  {type:"b", class:"x", value:"r"},
  {type:"a", class:"y", value:"p"}
];

I need to use Array.includes to check whether an object with class=y is in this array.

I need to check it with myarr.includes({condition});

I could simply pare the whole object but I don't know how to use a key of the object to check.

I have an Array, like this one:

let myarr = [
  {type:"a", class:"x", value:"p"},
  {type:"b", class:"x", value:"r"},
  {type:"a", class:"y", value:"p"}
];

I need to use Array.includes to check whether an object with class=y is in this array.

I need to check it with myarr.includes({condition});

I could simply pare the whole object but I don't know how to use a key of the object to check.

• javascript
• arrays

• it does not work with includes. you need a different approach. why includes? – Nina Scholz Commented Sep 6, 2018 at 11:13
• Why are you using .includes() for that? Is this a requirement? –  Commented Sep 6, 2018 at 11:13
• Why would you need to check it with myarr.includes? Thats not the right method for the job – Luca Kiebel Commented Sep 6, 2018 at 11:13
• myarr.some(x=>x.class=='y')?? – Jaydip Jadhav Commented Sep 6, 2018 at 11:14

6 Answers 6

To do this you can use the some() method.

The some() method tests whether at least one element in the array passes the test implemented by the provided function.

let myarr = [
  {type: "a",class: "x",value: "p"},
  {type: "b",class: "x",value: "r"},
  {type: "a",class: "y",value: "p"}
];

let pass = myarr.some(item => item.class == 'y');
let fail = myarr.some(item => item.class == 'z');

console.log(pass);
console.log(fail);

Array.prototype.includes relies on identity checks which requires you to pass in the same object (not just an object with the same properties, it needs the same reference such that objA === objB). You want a function that allows you to provide a function in which you can check the condition. Fortunately there is Array.prototype.some for this ask.

myarr.some(item => item.class === 'y')

You may either use Array#some or you may also take advantage of using proper data structures.

Array#some

const myArr = [{
    type: "a",
    class: "x",
    value: "p"
  },
  {
    type: "b",
    class: "x",
    value: "r"
  },
  {
    type: "a",
    class: "y",
    value: "p"
  }
]

const hasClassY = myArr.some (o => o.class == 'y')
console.log (hasClassY)

Map instead of Array

const classMap = new Map([
  ['x', [{
    type: "a",
    class: "x",
    value: "p",

  }, {
    type: "b",
    class: "x",
    value: "r"
  }]],

  ['y', [{
    type: "a",
    class: "y",
    value: "p"
  }]]
])

if (classMap.has('y')) {
  // Do stuff here
}

const itemsWithYClass = classMap.get('y')
const itemsWithXClass = classMap.get('x')

const flatten = xs => [...xs].reduce((r, el) => [...r, ...el])

const allItems = flatten(classMap.values())

console.log('Y class: ', itemsWithYClass)
console.log('X class: ', itemsWithXClass)
console.log('All: ', allItems)

Specialized Map

class SpecializedMap extends Map {
  get[Symbol.species]() {
    return Map
  }

  getAll() {
    return [...this.values()].reduce((r, el) => [...r, ...el])
  }
}


const classMap = new SpecializedMap([
  ['x', [{
    type: "a",
    class: "x",
    value: "p",

  }, {
    type: "b",
    class: "x",
    value: "r"
  }]],

  ['y', [{
    type: "a",
    class: "y",
    value: "p"
  }]]
])

if (classMap.has('y')) {
  // Do stuff here
}

const itemsWithYClass = classMap.get('y')
const itemsWithXClass = classMap.get('x')
const allItems = classMap.getAll()


console.log('Y class: ', itemsWithYClass)
console.log('X class: ', itemsWithXClass)
console.log('All: ', allItems)

Array + Set

const myArr = [{
    type: "a",
    class: "x",
    value: "p"
  },
  {
    type: "b",
    class: "x",
    value: "r"
  },
  {
    type: "a",
    class: "y",
    value: "p"
  }
]

// This set contains all unique classes within myArr
// The challenge is you need to sync myArr with classSet
// so classSet contains the actual classes within myArr.
const classSet = new Set(['x', 'y'])

// Somewhere in your code you import classSet and...

if (classSet.has('y')) {
  console.log('Do stuff here!')
}

Try this simple solution.

let myarr = [
  {type:"a", class:"x", value:"p"},
  {type:"b", class:"x", value:"r"},
  {type:"a", class:"y", value:"p"}
];

console.log(myarr.some(function(element){return element["class"] === "x";}))

You could use Array.prototype.includes() or String.prototype.includes() but is not practical, and is not useful as a general solution in this case, see this:

let myarr = [
    {type:"a", class:"x", value:"p"},
    {type:"b", class:"x", value:"r"},
    {type:"a", class:"y", value:"p"}
  ];

//String.includes - We need the exact match, this could lead to error  
var value1 = JSON.stringify(myarr).includes('"class":"x"');

//Array.includes - It's ok, but it has two iterations, not one as some()
var value2 = myarr.map(o=>o.class).includes("x")

console.log(value1)
console.log(value2)

That is why using Some(), as other users said, is the better choice.

I use lodash .includes() or .has() methods for things like that:

_.includes({ 'a': 1, 'b': 2 }, 1);

https://lodash./docs/4.17.10#includes

You can also do this with a plain js map, some or other methods.