JS Replace variable reference in string with the variable contents

Question

I want create a function which takes a string parameter and replaces variable references within it (designated with flanking %'s) with their corresponding variable values. I have been sufficiently warned about risk of eval() function, but haven't found an alternative. I am not sure how risky this code is. If it is a problem, what approach would be more secure.

Here is what I have:

var a = 1;
var b = 2;
result = myFunction("a is %a%, b is %b%");
console.log(result); // return "a is 1, b is 2"

function myFunction(text) {
    // escape needed chars in text for regex
    text = text.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
    var regExp = /%.+?%/g,
        match;
    while (match = regExp.exec(text)) {
        rep = match[0].substr(1).slice(0, -1); // remove flanking %'s
        text = text.replace(match[0], eval(rep));
    }
    return text
}

Based upon MH Souza recommendation, I figured this should work, but output is:

%a% a
%b% b
a is a, b is b

var a = 1;
var b = 2;
result = myFunction("a is %a%, b is %b%");
console.log(result);

function myFunction(text) {
  // escape neede chars in text for regex
  text = text.replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");
  var regExp = /%.+?%/g,
    match;
  while (match = regExp.exec(text)) {
    var rep = match[0].substr(1).slice(0, -1); // remove flanking %'s
    var rep = `${rep}`;
    console.log(match[0], rep);
    text = text.replace(match[0], rep);
  }
  return text
}

Do you have any constraints that prevent you from using template literals? — rishat
– rishat, Commented Oct 28, 2017 at 19:36
Other than never using them before and not quite knowing how to implement, I no contraints. — cycle4passion
– cycle4passion, Commented Oct 28, 2017 at 20:05

Matheus Henrique Souza · Accepted Answer · 2017-10-28 21:06:33Z

3

You can achieve this by using Template Literals.

In your case:

const a = 1;
const b = 2;
const result = `a is ${a}, b is ${b}`; // a is 1, b is 2

You just need to write your string like this: `My string`

And to concatenate a variable value, you write the variable like this: ${myVariable}

So, the final result would look like this:

const myVariable = 'awesome';
const finalResult = `My string is ${myVariable}` // My string is awesome

answered Oct 28, 2017 at 21:06

Matheus Henrique Souza

1465 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

cycle4passion Over a year ago

code updated above, still not resolving like I would expect.

Collectives™ on Stack Overflow

JS Replace variable reference in string with the variable contents

1 Answer 1

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related