Underscore.js _.isWeakMap() Function

Last Updated : 25 Nov, 2021

Underscore.js is a library in javascript that makes operations on arrays, string, objects much easier and handy. _.isWeakMap() function is used to check whether the given object is javascript weakmap or not. When linking the underscore.js CDN The "_" is attached to the browser as global variable.

Syntax:

_.isWeakMap(object);

Parameters :

object: It is any javascript object such as array, string, maps, set etc.

Returns: It returns the boolean value. If the object is a weak map of javascript it returns true otherwise false is returned by the function.

Few Examples are given below for a better understanding of the function.

Example 1: When an array is given the output is false.

javascript

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charMap="UTF-8">
  <meta name="viewport" 
        content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src=
"https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js" > 
  </script> 
</head>
<body>
  <script>
    //creating a array of size 2 using constructor
    var obj= new Array(2);
    //filling value 10in the array
    obj.fill(5)
    //using the underscore.js function _.weakMap()
    var isWeakMap= _.isWeakMap(obj);
    console.log(isWeakMap)
    //If the given object is weakMap it prints the object is weak Map.
    if(isWeakMap)
    console.log(`The ${obj} is the WeakMap of Javascript.`)
    else
    console.log(`The ${obj} is not the WeakMap of Javascript.`)
  </script>
</body>
</html>

Output:

Example 2:

When a weak set is given it returns true.

javascript

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charMap="UTF-8">
  <meta name="viewport" 
        content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <script src=
"https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js" > 
  </script> 
</head>
<body>
  <script>
    //creating a array of size 2 using constructor
    var obj= new WeakMap();
    //using the underscore.js function _.weakMap()
    var isWeakMap= _.isWeakMap(obj);
    console.log(isWeakMap)
    //If the given object is weakMap it prints the object is weak Map.
    if(isWeakMap)
    console.log(`The ${obj} is the WeakMap of Javascript.`)
    else
    console.log(`The ${obj} is not the WeakMap of Javascript.`)
  </script>
</body>
</html>