Google Closure Compiler is importing my extern functions - google-closure-compiler

Question

I have created an extern in a javascript file and specified it as part of the Google Closure Compiler (GCC) command line option. I am compiling with advanced mode. GCC is taking the function in my extern and placing it in the compiled code. I have no idea why it would do this. GCC is suppose to recognize that the extern function is in a separate file. When I export the object, it will rename the object and leave the object's function names alone BUT it will create a copy of the entire extern function in the compiled code.
I have tried many variations (too numerous here to list) to see how to prevent GCC from doing this but nothing has worked.
My extern:
var MyCustomResizer = {
"onResize": function (a, b) {
},
"detach": function () {
}
}
I exported the object as follows:
window["MyCustomResizer"] = MyCustomResizer;
My app using the "detach" function:
MyCustomResizer.detach();
My compiler settings:
java -jar closure-compiler/compiler.jar \
--compilation_level ADVANCED_OPTIMIZATIONS \
--externs scripts/externs/resizer-extern.js \
--js_output_file scripts/release/myapp.js \
--warning_level VERBOSE \
--language_out ECMASCRIPT5 \
--language_in=ECMASCRIPT_2017 \
--js scripts/base.js
And the generated compiled output contains this:
ha.detach();
...
var ha = {
onResize: function () {
}, detach: function () {
}
};

Answer 1

It turns out that when you specify extern files, you MUST use the --extern option in front of every extern file. I only had it on the first one:
Incorrect:
java -jar closure-compiler/compiler.jar \
--compilation_level ADVANCED_OPTIMIZATIONS \
--externs scripts/externs/jQuery/jquery-1.9-externs.js \
scripts/externs/third-party.js \
--js_output_file scripts/release/servetus-min.js \
Correct:
java -jar closure-compiler/compiler.jar \
--compilation_level ADVANCED_OPTIMIZATIONS \
--externs scripts/externs/jQuery/jquery-1.9-externs.js \
--externs scripts/externs/third-party.js \
--js_output_file scripts/release/servetus-min.js \
I find it very strange that the compiler just ignores the one without the --externs but just goes ahead anyway and copies its functions into the compiled code. This should not be allowed and a warning should be issued. This took an entire day to track down.