Text Processing with JavaScript

Recipe 40

Generating Indices for Matches with the d Flag

Task

Suppose you’re building a tool that helps detect errors and potential problems in JavaScript code. You need your tool to be able to detect the use of reserved words in variables and functions and warn the user.

Ideally, you want to program your tool to pinpoint the exact part of the code where the reserved word is misused rather than outputting just a line number. So, if the code has a variable assignment with a reserved word like this:

let default = 7;

You want to indicate the error like this:

let default = 7;
    ↑------ Invalid variable name

To achieve this task, you need a regex that provides the start and end indices of the match.

Solution

Send the supplied code one line ...