Parser API: Expose a Method to Determine Whether a Numeric Literal is of Certain Flag

<!-- 🚨 STOP 🚨 𝗦𝗧𝗢𝗣 🚨 𝑺𝑻𝑶𝑷 🚨 Half of all issues filed here are duplicates, answered in the FAQ, or not appropriate for the bug tracker. Please read the FAQ first, especially the "Common Feature Requests" section. --> ## Search Terms Parser API numericLiteralFlags numeric literal flag <!-- List of keywords you searched for before creating this issue. Write them down here so that others can find this suggestion more easily --> ## Suggestion Currently the parser API apparently does not expose `numericLiteralFlags` for determining whether the original source is written using features such as binary or octal literal. I have to do this to determine whether the original source was written using ECMAScript 2015 numeric literal: ```ts if (TypeScript.isNumericLiteral(node)) { let bitflag = node['numericLiteralFlags']; if (bitflag) { if (bitflag & (1 << 8)) { // internal flag: Octal // https://github.com/Microsoft/TypeScript/blob/a4a1bed88bdcb160eff032790f05629f9fa955b4/src/compiler/types.ts#L1659 return true; } if (bitflag & (1 << 7)) { // internal flag: Binary // https://github.com/Microsoft/TypeScript/blob/a4a1bed88bdcb160eff032790f05629f9fa955b4/src/compiler/types.ts#L1658 return true; } } } ``` AFAIK this is the only way to check it since `node.text` evaluates to the string representation of the base 10 number... ## Use Cases I need this 'internal' API to write [a parser for helping determine whether a JS file is compatible with syntax of certain ECMAScript version](https://github.com/ryanelian/instapack/blob/terser/src/SyntaxLevelChecker.test.ts). For example: Can this script run in ES5 environments? `node_modules` may contain packages not distributed in ES5, which can cause minification error when being minified with minifier not capable of handling ES5, or worse, ninja runtime error. …