use of ['mobile' + param.charAt(0).toUpperCase() + param.slice(1)]: 4

Question

I am not able to understand the given line of code:-
['mobile' + param.charAt(0).toUpperCase() + param.slice(1)]: 4

FULL CODE:-

var param = 'size';
var config = {
[param]: 12,
['mobile' + param.charAt(0).toUpperCase() + param.slice(1)]: 4
};

console.log(config.mobileSize);

Answer 1

it's the new ES6’s “Computed Property Names” feature that allows you to have an expression (a piece of code that results in a single value like a variable or function invocation) be computed as a property name on an object.

have look at → https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Object_initializer#Computed_property_names