Shared Polyfills in Google Closure Compiler

Question

I'm trying to achieve following use case:

my codebase is split to 3 JavaScript files: A, B and C
files B and C both depends on file A (meaning they are e.g. calling methods declared in A)
all files are using ES2015 (ES6) code

I'm using Google Closure Compiler to transpile them to ES5 and minify them. Which works fine with following configuration of NPM module google-closure-compiler:

default: {
            files: {
              "A.min.js" : "A.js",
              "B.min.js" : "B.js",
              "C.min.js" : "C.js",
            },
            options: {
                compilation_level: "SIMPLE",
                language_in: "ES6_STRICT",
                language_out: "ES5_STRICT"
            }
        }

But I'd like to optimize it. The configuration above causes that Closure Compiler 'injects' the same polyfill to all 3 files where needed (e.g. if A and C are using WeakMap, then both A.min and C.min contain polyfill for WeakMap).

My question is, is there a way to force the compiler to put common polyfills in only A? Something like if B or C are using WeakMap, then if A is using WeakMap, put polyfill to A. If A is not using WeakMap, put polyfills to B and C as usual?

score 1 · Answer 1 · edited May 23 '17 at 12:26

The best option is to use the code splitting functionality of the compiler to have a single compilation. The polyfills should only be injected into the base file then. See How do I split my javascript into modules using Google's Closure Compiler? for examples.

If you want to keep using separate compilations, there are two non-publicized flags that can help:

Shared Polyfills in Google Closure Compiler

1 Answers1