Javascript & regular expression

Question

I have this string

java=10514;js=237;jsp=3995;web=5;xml=42

and I'd like to extract, in separate variables, the value numbers for each language, using javascript and a regular expression that is, for the "java" case, the follow

(?<=java=).*?(?=;|$)

I've tried this code

var myString = "java=10514;js=237;jsp=3995;web=5;xml=42";
var regexp_java = new RegExp('(?<=java=).*?(?=;|$)', 'g');    
var ncloc_java = sonar_myString.match(regexp_java);
var regexp_js = new RegExp('(?<=js=).*?(?=;|$)', 'g');    
var ncloc_js = sonar_myString.match(regexp_js);
var regexp_jsp = new RegExp('(?<=jsp=).*?(?=;|$)', 'g');    
var ncloc_jsp = sonar_myString.match(regexp_jsp);
var regexp_web = new RegExp('(?<=web=).*?(?=;|$)', 'g');    
var ncloc_web = sonar_myString.match(regexp_web);
var regexp_jsp = new RegExp('(?<=jsp=).*?(?=;|$)', 'g');    
var ncloc_jsp = sonar_myString.match(regexp_jsp);

but it doesn't work.

Any suggestion will be appreciated and thank you in advance

Any reason it **has** to be regex, rather than simple string manipulation? — VLAZ, Dec 27 '22 at 08:43

score 3 · Accepted Answer · answered Dec 27 '22 at 08:46

3

I believe that you are using the wrong data structure here. Rather than trying to use individual variables for each language, you can instead use a hashmap. First split to the string on semicolon, and then stream that to get each language and value.

var input = "java=10514;js=237;jsp=3995;web=5;xml=42";
var map = {};
input.split(";").forEach(x => map[x.split("=")[0]] = x.split("=")[1]);
console.log(map);

answered Dec 27 '22 at 08:46

Tim Biegeleisen

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Hi there, all is well? Do you agree with the duplicate here? – The fourth bird Jan 07 '23 at 14:25
1

@Thefourthbird As a matter of fact, no, I don't. That duplicate doesn't really cover this question. – Tim Biegeleisen Jan 07 '23 at 15:01

score 2 · Answer 2 · answered Dec 27 '22 at 08:56

Does it really need to be done with Regex? Anyways I'm providing you with 2 solutions.

const string = "java=10514;js=237;jsp=3995;web=5;xml=42";

let result1 = string.split(';').reduce((acc, curr) => {
  let [key, value] = curr.split('=');
  acc[key] = value;
  return acc;
}, {});

console.log(result1);

let result2 = {};
let regex = /([a-z]+)\s*=\s*(\d+)/g;
let check;

while (check= regex.exec(string)) {
  result2[check[1]] = check[2];
}

console.log(result2);

score 2 · Answer 3 · answered Dec 27 '22 at 09:27

2

You don't have to create separate patterns and variables, Instead you can use 2 capture groups and then create an object with keys and values (assuming there are no duplicate keys)

\b(java|jsp?|web|xml)=([^;\s]+)

Explanation

\b A word boundary
(java|jsp?|web|xml) Match one of the alternatives
= Match literally
([^;\s]+) Capture group 2, match 1+ chars other than a whitespace char or ;

See a regex demo.

const myString = "java=10514;js=237;jsp=3995;web=5;xml=42";
const regex = /\b(java|jsp?|web|xml)=([^;\s]+)/g;
const kv = Object.fromEntries(
  Array.from(
    myString.matchAll(regex), m => [m[1], m[2]]
  )
)
console.log(kv)
console.log(kv.java);

answered Dec 27 '22 at 09:27

The fourth bird

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Hey buddy, nice code. Could you please explain it from `Object.fromEntries` to its completion. Trying to learn JS but not able to fully understand it. I get that you are doing it in 2 capturing groups and putting output into key value pair format but how its working inside JS thing not sure. Will be grateful to you, Thank you. – RavinderSingh13 Jan 02 '23 at 06:19
1

@RavinderSingh13 Hey man, yes of course. The [Object.fromEntries()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/fromEntries) `transforms a list of key-value pairs into an object` The [Array.from()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/from) `creates a new, shallow-copied Array instance from an iterable or array-like object.` – The fourth bird Jan 02 '23 at 13:04
1

The [String.prototype.matchAll()](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/matchAll) `method returns an iterator of all results matching a string against a regular expression, including capturing groups.` So `matchall` returns the iterator with the 2 capture group values to `Array.from`, which returns an array of arrays which looks like `[["java","10514"],["js","237"]]` That is a datastructure that Object.fromEntries can process to create an object with key-value pairs. – The fourth bird Jan 02 '23 at 13:05
1

Thank you buddy, let me process these comments, thank you for detailed explanation, let us keep these for future users if you ok with it, cheers ++ – RavinderSingh13 Jan 02 '23 at 13:13
Hey, one more question could you please do explain more on `m => [m[1], m[2]]` code? I am not that expert in JS so need to completely understand it, thank you buddy for your help cheers. – RavinderSingh13 Jan 02 '23 at 13:44
1

@RavinderSingh13 This whole part `m => [m[1], m[2]]` is a function that is passed as the second parameter to `Array.from()` as the inline mapping function. The outer square brackets here `[...]` create an array that will hold the 2 values, where `m[1]`is the capture group 1 value, and `m[2]` the capture group 2 value. So we are basically mapping each item of result from matchAll to an array of array's (where each inner array has 2 values) – The fourth bird Jan 02 '23 at 14:04

Javascript & regular expression

3 Answers3