Underscore.js _.constant() Function

Last Updated : 10 Jul, 2020

Underscore.js is a JavaScript library that makes operations on arrays, string, objects much easier and handy. The _.constant() function is used to create a function that returns the parameter given to it. It is almost same as _.identity() function.

Note: It is very necessary to link the underscore CDN before going and using underscore functions in the browser. When linking the underscore.js CDN, the "_" is attached to the browser as global variable.

Syntax:

_.constant( object );

Parameters: This function accepts single parameter object.

Return Value: This function returns the parameter as given to the function.

Below examples illustrate the _.constant() function in Underscore.js:

Example 1:

html

<!DOCTYPE html>
<html>

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

<body>
    <script>

        let str = "geeksforgeeks"

        // _.constant function of underscore.js
        let strFunc = _.constant(str);
        console.log(`original str is: ${str}`)
        console.log(`str Function is: ${strFunc}`)

        // This will return true
        console.log(str === strFunc())

        // Both strings are exactly same
        console.log("from str : ", str, 
            " from strFunc: ", strFunc());
    </script>
</body>

</html>

Output:

Example 2:

html

<!DOCTYPE html>
<html>

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

<body>
    <script>

        // Creating a object
        let obj = {
            "a": "one",
            "b": "two",
            "c": "three"
        }

        // _.constant function of underscore.js
        let objFunc = _.constant(obj);
        console.log(`original object is: ${obj}`)
        console.log(`object Function is: ${objFunc}`)

        // This will return true
        console.log(obj === objFunc())

        // Both objects are exactly same
        console.log("from obj : ", obj.a, 
            " from objFunc: ", objFunc().a);

        // Made Changes in object
        obj.a = 12

        // Change in one object reflects
        // in another
        console.log("change in one object "
                + "reflects in another =>")
                
        console.log("from obj : ", obj.a, 
            " from objFunc: ", objFunc().a);
    </script>
</body>

</html>