Question

59

How to check if Javascript Map has an object key

rated 0 times [ 65] [ 6] / answers: 1 / hits: 39763 / 7 Years ago, thu, july 6, 2017, 12:00:00

Looking at a couple of different docs, all I see is when the Map (ECMAScript6) key is a boolean, string, or integer. Is there a way we could use another customized Object (called with the new CustomObject(x,y) constructor call) to be added as a key?

I am able to add an object as a key, but unable to check if the Map has the said object.

var myMap = new Map();

myMap.set( new Tuple(1,1), foo);

myMap.set('bar', foo);





myMap.has(?);  

myMap.has('bar');  // returns true

Is there a way around this?

  var myMap = new Map();

  myMap.set( new Tuple(1,1), foo);



 for(some conditions) {

 var localData = new Tuple(1,1); //Use directly if exists in myMap? 

 map.has(localData) // returns false as this is a different Tuple object. But I need it to return true

}

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map/has

Answers

Only authorized users can answer the question. Please sign in first, or register a free account.

aden

Add To Favorites

Follow

Total Points: 369

Total Questions: 100

Total Answers: 83

Location: Australia

Member since Tue, Oct 19, 2021

3 Years ago

answered 7 Years ago harleyaleenag · Accepted Answer

You just have to save the reference to the object:

var myMap = new Map();

var myKey = new Tuple(1,1);

myMap.set( myKey, foo);

myMap.set('bar', foo);



myMap.has(myKey);           // returns true;  myKey === myKey

myMap.has(new Tuple(1,1));  // returns false; new Tuple(1,1) !== myKey

myMap.has('bar');           // returns true;  'bar' === 'bar'

Edit: Here is how to use an object to achieve what you want, which is to compare objects by their values rather than by reference:

function Tuple (x, y) {

  this.x = x;

  this.y = y;

}

Tuple.prototype.toString = function () {

  return 'Tuple [' + this.x + ',' + this.y + ']';

};



var myObject = {};

myObject[new Tuple(1, 1)] = 'foo';

myObject[new Tuple(1, 2)] = 'bar';

console.log(myObject[new Tuple(1, 1)]); // 'foo'

console.log(myObject[new Tuple(1, 2)]); // 'bar'

These operations will run in constant time on average, which is much faster than searching through a Map for a similar object key in linear time.