Javascript convert PascalCase to underscore_case/snake_case

How can I convert PascalCase string into underscore_case/snake_case string? I need to convert dots into underscores as well.

eg. convert

TypeOfData.AlphaBeta

into

type_of_data_alpha_beta

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(/^_/, ""));
  

OR

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(/^_/, ""));

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);

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.

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

"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 )

This will get you pretty far: https://github.com/domchristie/humps

You will probably have to use regex replace to replace the "." with an underscore.

I found this but I edited it so suit your question.

const camelToSnakeCase = str => str.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`).replace(/^_/,'')

Good examples for js:

1. Snake Case
2. Kebab Case
3. Camel Case
4. Pascal Case

have here

function toCamelCase(s) {
  // remove all characters that should not be in a variable name
  // as well underscores an numbers from the beginning of the string
  s = s.replace(/([^a-zA-Z0-9_\- ])|^[_0-9]+/g, "").trim().toLowerCase();

  // uppercase letters preceeded by a hyphen or a space
  s = s.replace(/([ -]+)([a-zA-Z0-9])/g, function(a,b,c) {
    return c.toUpperCase();
  });

  // uppercase letters following numbers
  s = s.replace(/([0-9]+)([a-zA-Z])/g, function(a,b,c) {
    return b + c.toUpperCase();
  });

  return s;
}

Try this function, hope it helps.

"TestString".replace(/[A-Z]/g, val => "_" + val.toLowerCase()).replace(/^_/,"")

replaces all uppercase with an underscore and lowercase, then removes the leading underscore.

A Non-Regex Answer that converts PascalCase to snake_case

Note: I understand there are tons of good answers which solve this question elegantly. I was recently working on something similar to this where I chose not to use regex. So I felt to answer a non-regex solution to this.

const toSnakeCase = (str) => {
    return str.slice(0,1).toLowerCase() + str.split('').slice(1).map((char) => {
        if (char == char.toUpperCase()) return '_' + char.toLowerCase();
        else return char;
    }).join('');
}

Eg.

inputString = "ILoveJavascript" passed onto toSnakeCase()

would become "i_love_javascript"