Check an array contains an object using one key with Array.includes

Question

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

Answer 1

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); 

Answer 2

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')

Answer 3

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!') } 

Answer 4

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";})) 

Answer 5

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.

Answer 6

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

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

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

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