How to check if a string ONLY contains specific strings

Question

I want to test if a string ONLY contains specific substrings (as whole words) / spaces

I've written some code and it works, but I am concerned that I don't understand the regex (I've copied from elsewhere)

Is there a way of doing this without complex regex?

const str1 = 'a♭ apple a a a a a apple   a♭ a'; // valid
const str2 = 'a♭ apple a a a a a apple   a♭ aa'; // invalid aa
const str3 = 'a♭ apple ad  a a a apple   a♭ a'; // invalid ad
const str4 = ' a♭ apple a a a a a apple   a♭ a'; // valid
const str5 = ' a♭ apple a a a a a apple   a♭ a '; // valid
const str6 = 'a♭ apple a a a a a apple   a♭ a '; // valid
const str7 = '      '; // invalid
const str8 = ''; // invalid

const allowedSubstrings = [
  'a', 'a♭', 'apple'
]

const isStringValid = str => {
  if (str.trim() === '') return false
  allowedSubstrings.forEach(sub => {
    // https://stackoverflow.com/a/6713427/1205871
    // regex for whole words only
    const strRegex = `(?<!\\S)${sub}(?!\\S)`
    const regex = new RegExp(strRegex, 'g')
    str = str.replace(regex, '')
  })
  str = str.replaceAll(' ', '')
  // console.log(str)
  return str === ''
}

console.log('str1', isStringValid(str1))
console.log('str2', isStringValid(str2))
console.log('str3', isStringValid(str3))
console.log('str4', isStringValid(str4))
console.log('str5', isStringValid(str5))
console.log('str6', isStringValid(str6))
console.log('str7', isStringValid(str7))
console.log('str8', isStringValid(str8))

@danday74, this seems to work but im not sure im not able to extract capture group, maybe someone can build on this! ((?![apple|a|a♭| ]).)* done on regexr.com — Naren Murali
– Naren Murali, Commented Jan 2, 2024 at 5:55
@mandy8055 if there is a keyword matched, then it means its an invalid value right? — Naren Murali
– Naren Murali, Commented Jan 2, 2024 at 6:08
@mandy8055 I think its wrong what I made, appologies for confusion! — Naren Murali
– Naren Murali, Commented Jan 2, 2024 at 6:27
Do you also want to match an empty string? (as your code currently does) — The fourth bird
– The fourth bird, Commented Jan 2, 2024 at 10:34
@Thefourthbird good point! I'm not sure of the answer myself yet but I'll check how my code works and fix if needed :) thx — danday74
– danday74, Commented Jan 4, 2024 at 2:29

mandy8055 · Accepted Answer · 2024-02-07 11:53:32Z

8

One approach which I can think of (which avoids complex regex) would be to:

split the string based on one or more whitespace characters (space, tabs or others)
check if every word in the words array (created by above split) is included in the allowedSubstrings array.

const str1 = 'a♭ apple a a a a a apple   a♭ a'; // valid
const str2 = 'a♭ apple a a a a a apple   a♭ aa'; // invalid aa
const str3 = 'a♭ apple ad  a a a apple   a♭ a'; // invalid ad
const str4 = ' a♭ apple a a a a a apple   a♭ a'; // valid
const str5 = ' a♭ apple a a a a a apple   a♭ a '; // valid
const str6 = 'a♭ apple a a a a a apple   a♭ a '; // valid
const str7 = '      '; // invalid
const str8 = ''; // invalid

const allowedSubstrings = [
  'a', 'a♭', 'apple'
];

const isStringValid = (str) => {
  const words = str.trim().split(/\s+/);
  // If the requirement would be to make them valid, we can use trim().
  // const words = str.trim().split(/\s+/);
  return words.every(word => allowedSubstrings.includes(word));
};

// const isStringValid = (str) => str.split(/\s+/).every(word => allowedSubstrings.includes(word));

console.log('str1', isStringValid(str1));
console.log('str2', isStringValid(str2));
console.log('str3', isStringValid(str3));
console.log('str4', isStringValid(str4));
console.log('str5', isStringValid(str5));
console.log('str6', isStringValid(str6));
console.log('str7', isStringValid(str7));
console.log('str8', isStringValid(str8));

edited Feb 7, 2024 at 11:53

answered Jan 2, 2024 at 5:27

mandy8055

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2 Comments

danday74 Over a year ago

much more intelligent than my approach - will accept if no1 comes up with a better answer shortly

danday74 Over a year ago

accepted this answer thx - added a trim() to your code after you pointed out failing test cases - many thx :)

M Junaid · Accepted Answer · 2024-01-02 07:27:15Z

3

A single regular expression pattern that checks whether the string contains only the specified substrings as whole words or spaces. It uses the join('|') method to create an alternation pattern (|) for the allowed substrings and then tests the string against this pattern using test().

const str1 = 'a♭ apple a a a a a apple   a♭ a'; // valid
const str2 = 'a♭ apple a a a a a apple   a♭ aa'; // invalid aa
const str3 = 'a♭ apple ad  a a a apple   a♭ a'; // invalid ad

const allowedSubstrings = [
  'a',
  'a♭',
  'apple'
];

const isStringValid = str => {
  const regex = new RegExp(`^((${allowedSubstrings.join('|')})(\\s+|$))+$`);
  return regex.test(str);
};

console.log('str1', isStringValid(str1));
console.log('str2', isStringValid(str2));
console.log('str3', isStringValid(str3));

edited Jan 2, 2024 at 7:27

answered Jan 2, 2024 at 7:17

M Junaid

9882 gold badges7 silver badges27 bronze badges

1 Comment

mandy8055 Over a year ago

This returns false for ' a♭ apple a a a a a apple a♭ a ' and ' a♭ apple ad a a a apple a♭ a' which as per OP should be true. You can fix this with the alternation with start of string too(^) though.

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