Capturing variable names using RegEX JavaScript?

Question

I am trying to capture variable names from the variable declaration. The variables are declared and initialized in the following manner:

let URL="https://www.lipsum.com/", error, pass=true;

I have this above code in the form of a string and I want to obtain the name of the variables using RegEX.

I am using this regex expression: /let\s+([\w_$]+)(?:=.*),?/;

However, I am only getting URL in the output

const str = `let URL="https://www.lipsum.com/", error, pass=true;`;
const regex = /let\s+([\w_$]+)(?:=.*),?/;

console.log(str.match(regex));

How do I obtain the variable names URL, error, and pass from the given string?

Yeah, A parser is also in my list, but parser like esprima, acorn, etc. have many other things and I have only a single requirement. So using a parser would be too much. — Shantanu Kaushik
– Shantanu Kaushik, Commented Jun 9, 2021 at 12:03

DecPK · Accepted Answer · 2021-06-10 10:44:52Z

3

You can first split it with , and then match it using regex

/(?:let)?\s*(\w+)(=.*)?/

const str = `let URL="https://www.lipsum.com/", error, pass=true;`;

const matches = str.split(",").map((s) => {
  const match = s.match(/(?:let)?\s*(\w+)(=.*)?/);
  return match[1];
});

console.log(matches);

EDIT: Some cases were not covered so I come up with one more solution

const str = `let abc123 , two,  three,
URL="https://www.lipsum.com/",
log,
error=[true, false],
pass=true,
obj={name: "test", nestedOBj: {a: 20}},
obj2 = [{}]
`;
const matches = str.split(",").flatMap((s) => {
  let match;
  if (s.includes("=")) {
    match = s.match(/(\w+)\s*(?=\=)/i);
    return match[1];
  } else if (!s.match(/[\[\]\{\}]/)) {
    return s.match(/(?:(?:let|const|var)\s+)?(\w+)/)[1];
  } else return [];
});

console.log(matches);

edited Jun 10, 2021 at 10:44

answered Jun 9, 2021 at 12:10

DecPK

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7 Comments

Shantanu Kaushik Over a year ago

Thanks this works, but it fails in one case ie. when we have a comma as a value for a variable or a value contains a comma. For example an array. But Your answers work for most of the cases. Thanks!

DecPK Over a year ago

I didn't get you, Please tell me so that I can edit the answer as per your requirement...

Shantanu Kaushik Over a year ago

if str =let URL="https://www.lipsum.com/", error=[true, false], pass=true; Then in this case the output will be URL, error, true, false, pass. But none and false are not variables.

DecPK Over a year ago

@ShantanuKaushik I've edited the answer. Please check and see if it covers all of your corner cases.

DecPK Over a year ago

I would be happier if you could come up with more corner cases, It will help me to identify corner cases better next time. Thanks

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