Google closure compiler and UMD pattern

问题

I am developing a javascript library which uses closure compiler to combine/minify & typecheck. To avoid pouting global namespace I want to use UMD pattern & closue @export(or goog.exportSymbol('workspace', lkr.workspace)

goog.provide('workspace');
goog.require('lkr.workspace');
/**
  * Exposed external access point
  * @export
  * @return {component}
  */
workspace = function() {
  return lkr.workspace.Core;
}

I have used an output-wrapper-file to generate the UMD wrapper

//UMD bundling closure code inside.
;(function (root, factory) {
    if (typeof define === 'function' && define.amd) {
        define([], factory);
    } else if (typeof module === 'object' && module.exports) {
        module.exports = factory();
    } else {
        root.workspace = factory();
  }
}(this, function () {
  %output%
  return workspace;
}));

Ref: https://medium.com/reflecting-on-bits/how-to-solve-missing-output-error-when-using-closure-compiler-7de6eac29776?swoff=true#.ntq9vav6s

Is this the correct approach for UMD pattern in closure, there seems to be internal support in the compiler to detect UMD but I can't find any examples. https://groups.google.com/forum/#!topic/closure-compiler-discuss/-M1HBUn35fs https://github.com/google/closure-compiler/pull/1048
I still get crashes seems workspace can't be located.

EXAMPLE

start.js

goog.provide('workspace');
/**
  * Exposed external access point
  * @export
  * @return {number}
  */
var workspace = function() {
  console.log('My workspace')
  return 0;
}

Compilation flags

closure_entry_point: 'workspace',
compilation_level: ADVANCED_OPTIMIZATION,
only_closure_dependencies: true,
generate_exports  :true,
language_in : 'ECMASCRIPT5_STRICT',
language_out : 'ES5_STRICT',

Output with UMD wrapper

(function(root, factory) {
    if (typeof define === 'function' && define.amd) {
        define([], factory);
    } else if (typeof exports === 'object') {
        module.exports = factory();
    } else {
        root.workspace = factory();
    }
}(this, function() {
    'use strict';
    'use strict';
    function a() {
        console.log("My workspace");
        return 0
    }
    var b = ["workspace"]
      , c = this;
    b[0]in c || !c.execScript || c.execScript("var " + b[0]);
    for (var d; b.length && (d = b.shift()); )
        b.length || void 0 === a ? c[d] ? c = c[d] : c = c[d] = {} : c[d] = a;
    return workspace;
}));

Error:

Uncaught TypeError: Cannot use 'in' operator to search for 'workspace' in undefined
Uncaught ReferenceError: workspace is not defined

回答1:

The only native support for the UMD pattern the compiler has is with the --process_common_js_modules. That flag is used to bundle modules together and will remove the pattern - so not what you want.

Your problems are with your output wrapper. The compiler attempts to export workspace by creating it as a property on the global this object. Your output wrapper doesn't specify a this object. Since you are in strict mode, it's also not auto-coerced to the global this object.

Update your output wrapper to something like:

//UMD bundling closure code inside.
;(function (root, factory) {
  if (typeof define === 'function' && define.amd) {
    define([], factory);
  } else if (typeof module === 'object' && module.exports) {
    module.exports = factory();
  } else {
    root.workspace = factory();
  }
}(this, function () {
  %output%
  return workspace;
}.bind(this));

来源：https://stackoverflow.com/questions/39847332/google-closure-compiler-and-umd-pattern

标签

javascript

google-closure-compiler

umd