How to use a variable in regex while checking for anything thats not a number or the variable

I have this JavaScript code:

let separator = '.';
let fee = '10.00';
let regex = new RegExp(/^[^a-zA-Z]*\.[^a-zA-Z]*$/);

console.log( regex.test( fee ) );

I want this to return false if the fee contains anything that isn’t a number and/or doesn’t contain the . separator.

1. How can I make the regex use the string from the separator variable, rather than hardcoding it directly in the regex like I have currently
2. How can I alter this regex to check for anything thats not a number and the separator, e.g. !@£$%^, currently it only does a-zA-Z

>Solution :

You can use the tick ` and then use a template literal expression: ${separator}.

• You must double escape values in a string regular expression.
• You no longer need to start/end the expression with /
• Instead of testing for all characters using [^a-zA-Z], test for digits using \d
• we need to escape the separator as . stands for anything.

let separator = '.';
let fee = '10.00';
let regex = new RegExp(`^\\d+\\${separator}\\d+$`);

console.log( regex.test( fee ) );         // True
console.log( regex.test( fee + 'abc' ) ); // False
console.log( regex.test( '1,23' ) );      // False
console.log( regex.test( '!@£$%^' ) );    // False

Here we change the separator to a comma, and now only the comma returns true:

let separator = ',';
let fee = '10.00';
let regex = new RegExp(`^\\d+\\${separator}\\d+$`);

console.log( regex.test( fee ) );         // False
console.log( regex.test( fee + 'abc' ) ); // False
console.log( regex.test( '1,23' ) );      // True
console.log( regex.test( '!@£$%^' ) );    // False

Note: if you need to have multiple separators in the same string, you could use the following:

`^\\d+[${separator}\\d]+\\d+$`