Underscore.js _.constant() Function

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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:

<!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 = "zambiatek" 
  
        // _.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:

<!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> 

Output:

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