Underscore.js _.isWeakSet() Function

Last Updated : 10 Jul, 2020
Underscore.js is a JavaScript library that makes operations on arrays, string, objects much easier and handy. he _.isWeakSet() function is used to check whether the given object is JavaScript weakset or not. When linking the underscore.js CDN, the "_" is attached to the browser as global variable. Syntax : 
_.isWeakSet( object );
Parameters:
  • object: It is any JavaScript object such as array, string, maps, set etc.
Return Value: It returns the boolean value. If the set is a weak set it returns true otherwise returns false. Example 1: When a weak set is given it returns true. html 
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content=
        "width=device-width, initial-scale=1.0">

    <script src=
"https://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.9.1/underscore-min.js">
    </script>
</head>

<body>
    <script>

        // Creating a weak set using
        // constructor
        var obj = new WeakSet();

        // Using the _.weakSet() function
        var isWeakSet = _.isWeakSet(obj);
        console.log(isWeakSet)

        // If the given object is weakset 
        // it prints the object is weak set.
        if (isWeakSet)
            console.log(`The ${obj} is the 
                    WeakSet of Javascript.`)
        else
            console.log(`The ${obj} is not 
                the WeakSet of Javascript.`)
    </script>
</body>

</html>
Output: Example 2: When an array is given the output is false. html 
<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content=
        "width=device-width, initial-scale=1.0">

    <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(10)

        // Using the _.weakSet() function
        var isWeakSet = _.isWeakSet(obj);
        console.log(isWeakSet)

        // If the given object is weakset 
        // it prints the object is weak set
        if (isWeakSet)
            console.log(`The ${obj} is the
                WeakSet of Javascript.`)
        else
            console.log(`The ${obj} is not 
                the WeakSet of Javascript.`)
    </script>
</body>

</html>
Output:
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