Regex: Matching the first letter(s) of multiple words

So I am really bad at regex stuff ... I googled for an hour now and the best answer I could find is this one.

But I still can't for the sake of me figure it out ...

What I need is the following:

I have a JS array I need to .filter() . This arrays contains for example:

[ 'Gurken halbiert 2kg', 'Karotten geschnitten 5kg', 'Gurken RW' ]

For example: All of the following inputs should match the first entry ( "Gurken halbiert 2kg" ):

"Gu ha"

"gur h"

"gu halbi"

The following inputs should not match it:

"ken halbi"

"urk ha"

"gur biert"

Why? because one or more letters at the beginning of any word are missing.

More example inputs and the entries they should match:

input: "Gur" -> matches 1st and 3rd entry

input: "Kar g 5" -> matches 2nd

input: "G r" -> matches 3rd

I really hope someone can help as I am totally lost in this RegEx chaos - I never really understood them or how to use them.

---

Since the input varies, you would need to dynamically generate the regular expression.

In the function below, you will notice that we are basically building a string and then creating the regular expression using new RegExp(string, 'i') .

The expression starts with a caret, and then basically follows the pattern:

^[[nth input char(s)]]w*s+[[nth input char(s)]]w*s+[[nth input char(s)]]w*

It's worth pointing out that w* is added after each input string and s+ is added if it's not the last input string (ie, not the end).

function generateRegex (input) {
  var string = '^', arr = input.trim().split(' ');
  arr.forEach(function (chars, i) {
    string += chars + 'w*' + (arr.length - 1 > i ? 's+' : '');
  });

  return new RegExp(string, 'i');
}

Then you can use the .filter() method on your array and return the elements that match:

var array = ['Gurken halbiert 2kg', 'Karotten geschnitten 5kg', 'Gurken RW'];
var filteredArray = array.filter(function (value) {
  return value.match(generateRegex('Gur Ha'));
});

---

Output:

'Gur Ha' would match: ["Gurken halbiert 2kg"]

'Gur' would match: ["Gurken halbiert 2kg", "Gurken RW"]

'Kar g 5' would match: ["Karotten geschnitten 5kg"]

'G r' would match: ["Gurken RW"]

---

Example:

function generateRegex (input) {
  var string = '^', arr = input.trim().split(' ');
  arr.forEach(function (chars, i) {
    string += chars + 'w*' + (arr.length - 1 > i ? 's+' : '');
  });

  return new RegExp(string, 'i');
}

var array = ['Gurken halbiert 2kg', 'Karotten geschnitten 5kg', 'Gurken RW'];
var filteredArray = array.filter(function (value) {
  return value.match(generateRegex('Gur'));
});

document.body.textContent = JSON.stringify(filteredArray);

---

Here is an example of how to filter user input as specified.

Notes

Escaping of regular expression characters from user input pattern (always sanitise user input).

Explicitly not using " w " in order to support characters like " é ".

Supports white space characters other than <space> like <tab> which can be copied and pasted into user input fields causing the user to think it's broken.

function doSubmit() {
  // Get the user input search pattern string 
  var userInput = document.getElementById("myinput").value,

    // List of strings to search
    testList = [
      'Gurken halbiert 2kg',
      'Karotten geschnitten 5kg',
      'Gurken RW'
    ],



    // Between our "words" we allow zero or more non-space characters "[^s]*"
    //  (this eats any extra characters the user might not have specified in their search pattern)
    // followed by one or more white-space characters "s+"
    //  (eating that space between the "words")
    // Note that we are escaping the "" characters here.
    // Note we also don't use "w" as this doesn't allow for characters like "é".
    regexBetween = '[^s]*s+',

    // Match the start of the string "^"
    // Optionally allow one or more "words" at the start
    //  (this eats a "word" followed by a space zero or more times).
    // Using an empty string here would allow "o g" to match the 2nd item in our test array.
    regexStart = '^(?:' + regexBetween + ')*',

    // Clean whitespace at begining and end
    regexString = userInput.trim()

      // Escape any characters that might break a regular expression
      // Taken from: https://developer.mozilla.org/en/docs/Web/JavaScript/Guide/Regular_Expressions
      .replace(/[.*+?^${}()|[]]/g, "$&")

      // Split into array of "words"
      .split(/s+/)

      // Combine the "words" building our regular expression string
      .join(regexBetween),

    // Create the regular expression from the string (non-case-sensitive 'i')
    regexObject = new RegExp(regexStart + regexString, 'i'),

    // Filter the input array testing for matches against the regular expression.
    resultsList = testList.filter(function(item) {
      return regexObject.test(item);
    });

  // Ouput the array into the results text area, one per line.
  document.getElementById('output').value = resultsList.join('n') + 'n===the end===';
}

<form id="myform" onsubmit="doSubmit(); return false;">
  <input type="text" id="myinput" value="" />
  <input type="submit" name="submit" />
</form>
<textarea id="output" rows="5" cols="30">
</textarea>

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