How can I check if an VALUE exists in MAP on Javascript?

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It looks a very easy question but i didnt find it in any place.

How can I know If an value exists in a Map?

For example:

A = [1,2,3,5,6,7]
var myMap = new Map();
    for (let i = 0; i < A.length; i++) {
    for (let z = 1; z < Number.MAX_SAFE_INTEGER; z++) {
            return z;

I want to check if, given one value, this VALUE is on the Hash. Like a "hasValue"

You can use iterate over the map, look for the value and return true (exiting the loop) as soon as you find it. Or you return false if the element does not exist. Something like:

const findInMap = (map, val) => {
  for (let [k, v] of map) {
    if (v === val) { 
      return true; 
  return false;

Map.has( ) In JavaScript, The Map.has() method in JavaScript is used to check whether an element with a specified key exists in a map or not. It returns a boolean value indicating the  Javascript Check If A Value Is In An Array Examples It’s relatively very easy in Javascript to check if a value is in an array. All you need is the array that you want to check and the value that you want to check against.

You cannot, other than by searching through it:


Use an appropriate data structure instead, like a set of all the values:

A = [1,2,3,5,6,7]
var myValues = new Set(A);

for (let z = 1; z < Number.MAX_SAFE_INTEGER; z++) {
    if(!myValues.has(z)) {
        return z;

Of course, given the fact that your A is sorted already, you could iterate it directly to find the lowest missing value.

Map.prototype.has(), Parameters. key: The key of the element to test for presence in the Map object. Return value. true if an element with the specified key exists in the Map object; otherwise false . In this tutorial, I show How you can check whether an Array already contains a specific value or not. This requires within the program in some cases like - Stop new value from insert if it already exists in an Array, execute script when the Array contains the particular value, etc..

I, personally prefers to find, indexOf and findIndex.

const array1 = (map, val) => {
  var foo;
  array2.find( (x) => foo = x === )
  return foo;




The Essential Guide to JavaScript Map: How To Use Maps Effectively, Prior to ES6, when you need to map keys to values, you often use an object, because an object To check if a key exists in the map, you use the has() method. To find out if a value exists at a given position index (where index is 0 or a positive integer), you literally just use However, it is possible for some array values to be null, undefined, NaN, Infinity, 0, or a whole host of different values.

Use Map.has(z), as described on MDN

Check if map contains value, in JS, JavaScript objects are hashmaps. Object.values converts a hashmap to a list of values. Array#indexOf finds the first location of a value in an array, or returns -1 if​  Is there any method other than running a for loop to check if a value exists in select box using JavaScript? I am looking for something like document.getElementById('selbox').valueExists('myval');

How to Check If a Value Exists in an Array in JavaScript, You can use the indexOf() method to check whether a given value or element exists in an array or not. The indexOf() method returns the index of the element  The has() method returns a boolean indicating whether an element with the specified key exists or not.

Map and Set, new Map() – creates the map. map.set(key, value) – stores the value by the the value by the key, undefined if key doesn't exist in map. map.has(key) To test keys for equivalence, Map uses the algorithm SameValueZero. How to check if a variable exists or defined in JavaScript. Topic: JavaScript / jQuery Prev|Next. Answer: Use the typeof operator. If you want to check whether a variable has been initialized or defined (i.e. test whether a variable has been declared and assigned a value) you can use the typeof operator.

JavaScript Array includes() Method, This method returns true if the array contains the element, and false if not. Note: The Check if an array includes "Banana", starting the search at position 3:. Returns the number of key/value pairs in the Map object. Methods Map.prototype.clear() Removes all key-value pairs from the Map object. Map.prototype.delete(key) Returns true if an element in the Map object existed and has been removed, or false if the element does not exist. Map.prototype.has(key) will return false afterwards. Map.prototype