Google Closure using ES5 strict mode even though I specified non-strict mode (in minify-maven-plugin configuration) - minify

Question

I'm using the com.samaxes.maven minify-maven-plugin to minify a collection of JS source files written using some of the ES6 features Google Closure supports. Here's the relevant configuration in my POM:
<!-- minify-maven-plugin: Minification using Google Closure -->
<plugin>
<groupId>com.samaxes.maven</groupId>
<artifactId>minify-maven-plugin</artifactId>
<version>1.7.6</version>
<executions>
<!-- Creation of the common-[version].js file -->
<execution>
<id>common-minify</id>
<phase>prepare-package</phase>
<configuration>
<charset>UTF-8</charset>
<jsSourceDir>.</jsSourceDir>
<jsSourceFiles>
...
</jsSourceFiles>
<jsFinalFile>./js/common-${project.version}.js</jsFinalFile>
<jsEngine>CLOSURE</jsEngine>
<closureLanguageIn>ECMASCRIPT6</closureLanguageIn>
<closureLanguageOut>ECMASCRIPT5</closureLanguageOut>
</configuration>
<goals>
<goal>minify</goal>
</goals>
</execution>
<!-- 2 other similarly configured executions are here. -->
...
</executions>
</plugin>
The problem is, when I run the maven goal this configuration, I get the following error message:
[INFO] Creating the merged file [common-1.8.24.js].
[INFO] Creating the minified file [common-1.8.24.min.js].
Jan 03, 2017 12:03:06 PM com.google.javascript.jscomp.LoggerErrorManager println
SEVERE: [1mcommon-1.8.24.js:5577: [31mERROR[39m - object literals cannot contain duplicate keys in ES5 strict mode[0m
supportsDataForwarding: function () {
^
This looks to me like Google Closure is trying to compile using ES5 Strict mode, even though I specified the non-strict ECMASCRIPT5 mode in my <closureLanguageOut> option (see doc here). Why is it not disabling strict mode?

Answer 1

i had the same problem and found a way to let the minify-maven-plugin not fail the build in case it complains about ES5 strict mode:
<plugin>
<groupId>com.samaxes.maven</groupId>
<artifactId>minify-maven-plugin</artifactId>
<version>1.7.6</version>
<executions>
<execution>
<id>default-minify</id>
<phase>process-resources</phase>
<configuration>
<charset>UTF-8</charset>
<closureWarningLevels>
<es5Strict>OFF</es5Strict>
</closureWarningLevels>
...
</configuration>
<goals>
<goal>minify</goal>
</goals>
</execution>
</executions>
You may further fine-tune using the following documentation How to tell closure compiler which warnings you want. Hope this helps :)