Javascript convert PascalCase to underscore_case/snake_case

Solution 1:

You could try the below steps.

Capture all the uppercase letters and also match the preceding optional dot character.
Then convert the captured uppercase letters to lowercase and then return back to replace function with an _ as preceding character. This will be achieved by using anonymous function in the replacement part.
This would replace the starting uppercase letter to _ + lowercase_letter.

Finally removing the starting underscore will give you the desired output.

var s = 'TypeOfData.AlphaBeta';
console.log(s.replace(/(?:^|\.?)([A-Z])/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));

var s = 'TypeOfData.AlphaBeta';
alert(s.replace(/\.?([A-Z])/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));

any way to stop it for when a whole word is in uppercase. eg. MotorRPM into motor_rpm instead of motor_r_p_m? or BatteryAAA into battery_aaa instead of battery_a_a_a?

var s = 'MotorRMP';
alert(s.replace(/\.?([A-Z]+)/g, function (x,y){return "_" + y.toLowerCase()}).replace(/^_/, ""));

Solution 2:

str.split(/(?=[A-Z])/).join('_').toLowerCase();

u're welcome

var s1 = 'someTextHere';
var s2 = 'SomeTextHere';

var o1 = s1.split(/(?=[A-Z])/).join('_').toLowerCase();
var o2 = s2.split(/(?=[A-Z])/).join('_').toLowerCase();

console.log(o1);
console.log(o2);

Solution 3:

Alternatively using lodash:

lodash.snakeCase(str);

Example:

_.snakeCase('TypeOfData.AlphaBeta');
// ➜ 'type_of_data_alpha_beta'

Lodash is a fine library to give shortcut to many everyday js tasks.There are many other similar string manipulation functions such as camelCase, kebabCase etc.

Solution 4:

This solution solves the non-trailing acronym issue with the solutions above

I ported the code in 1175208 from Python to JavaScript.

Javascript Code

function camelToSnakeCase(text) {
    return text.replace(/(.)([A-Z][a-z]+)/, '$1_$2').replace(/([a-z0-9])([A-Z])/, '$1_$2').toLowerCase()
}

Working Examples:

camelToSnakeCase('thisISDifficult') -> this_is_difficult

camelToSnakeCase('thisISNT') -> this_isnt

camelToSnakeCase('somethingEasyLikeThis') -> something_easy_like_this

Solution 5:

"alphaBetaGama".replace(/([A-Z])/g, "_$1").toLowerCase() // alpha_beta_gamma

Problem - Need to convert a camel-case string ( such as a property name ) into underscore style to meet interface requirements or for meta-programming.

Explanation This line uses a feature of regular expressions where it can return a matched result ( first pair of () is $1, second is $2, etc ).

Each match in the string is converted to have an underscore ahead of it with _$1 string provided. At that point the string looks like alpha_Beta_Gamma.

To correct the capitalization, the entire string is converted toLowerCase().

Since toLowerCase is a fairly expensive operation, its best not to put it in the looping handler for each match-case, and run it once on the entire string.

After toLowerCase it the resulting string is alpha_beta_gamma ( in this example )