guys pls i need your help it will be big help for me. i am angry and sad in same time i can't understand this section

Question

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

console.log(config.mobileSize); // 4

Answer 1

The second property is an array of String.
'mobile' + param.charAt(0).toUpperCase()
=> mobileS
mobileS + param.slice(1) -> slice will return all the elements from the position mentioned so it will get everything from 'i' in param.

So it becomes => 'mobileS' + 'ize'
Which is => mobileSize
And config.mobileSize is 4 which is nothing but the 2nd property of config.