Clasp: Automatically include polyfills for common methods that are valid typescript

Created on 7 May 2019 · 4Comments · Source: google/clasp

Not a bug-- feature proposal.

In my clasp projects, I often include a polyfill.js file that adds common ES6/ES7 methods to strings & arrays. For example:

String.includes
String.startswith
String.endswith
Array.includes

When writing GAS code in TypeScript, calling myString.startsWith("text") looks perfectly valid / doesn't raise any warnings in my editor, but when pushed & run GAS crashes, saying that function is not defined.

I think it could be a cool feature if clasp automatically detected some of those common methods being used in your code and created a polyfill.js, preventing run-time errors. I believe webpack does something like this?

Additionally / alternatively, clasp could warn you about methods in your code that won't run on GAS and can't be easily polyfilled.

I am willing to work on this if it seems like an appropriate addition!

Here is an example of a polyfill I often add:

polyfill.js

/**
 * Add "startsWith" method to strings
 * From: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/startsWith
 */
if (!String.prototype.startsWith) {
  Object.defineProperty(String.prototype, "startsWith", {
    value: function(search, pos) {
      pos = !pos || pos < 0 ? 0 : +pos;
      return this.substring(pos, pos + search.length) === search;
    }
  });
}

Source