Function Expression as a Constant Value in JavaScript

If the const is used in a program, and if you try to reassign the value to const variable then an error will arise.

Let’s say the following is our const variable −

const result = (first, second) => first * second;

Now, we will try to reassign a value to the const variable and an erro can be seen in the output.

Example

Following is the code −

const result = (first, second) => first * second;
result = first => first =first*10;
console.log(result(10,20)); 

To run the above program, you need to use the following command −

node fileName.js.

Here, my file name is demo284.js.

Output

This will produce the following output on console −

Error is visible “Assignment to constant variable” −

PS C:\Users\Amit\javascript-code> node demo284.js
C:\Users\Amit\javascript-code\demo284.js:2
result = first => first =first*10;
       ^
TypeError: Assignment to constant variable.
   at Object.<anonymous> (C:\Users\Amit\javascript-code\demo284.js:2:8)
   at Module._compile (internal/modules/cjs/loader.js:1133:30)
   at Object.Module._extensions..js (internal/modules/cjs/loader.js:1153:10)
   at Module.load (internal/modules/cjs/loader.js:977:32)
   at Function.Module._load (internal/modules/cjs/loader.js:877:14)
   at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:74:12)
   at internal/main/run_main_module.js:18:47

On commenting the below line, you will get the correct result −

// result = first => first =first*10;

Output

This will produce the following output on console −

PS C:\Users\Amit\javascript-code> node demo284.js
200