kata-6-solution-camelcase-to-underscore.js

// ************************************************************************************
// https://www.codewars.com/kata/camelcase-to-underscore/train/javascript

// You wrote all your unit test names in camelCase. But some of your colleagues have 
// troubles reading these long test names. So you make a compromise to switch to 
// underscore separation. To make these changes fast you wrote a class to translate 
// a camelCase name into an underscore separated name.

// Implement the ToUnderscore() method.
// Example:
// "ThisIsAUnitTest" => "This_Is_A_Unit_Test"

// But of course there are always special cases...
// You also have some calculation tests. Make sure the results don't get split by underscores. 
// So only add an underscore in front of the first number.
// Also Some people already used underscore names in their tests. You don't want to change them. 
// But if they are not split correct you should adjust them.
// Some of your colleagues mark their tests with a leading and trailing underscore. Don't remove this.
// And of course you should handle empty strings to avoid unnecessary errors. Just return an empty string then.

// Example:
// "Calculate15Plus5Equals20" => "Calculate_15_Plus_5_Equals_20"
// "This_Is_Already_Split_Correct" => "This_Is_Already_Split_Correct"
// "ThisIs_Not_SplitCorrect" => "This_Is_Not_Split_Correct"
// "_UnderscoreMarked_Test_Name_" => _Underscore_Marked_Test_Name_"
// ************************************************************************************


let toUnderScore = (name) => {
    return(name.replace(/\B([A-Z]|[0-9]+)/g, '_$1')).replace(/__/g,'_');
}