Use of const in strict mode : Azure Web App

Question

Application has thrown an uncaught exception and is terminated: SyntaxError: Use of const in strict mode.
    at Module._compile (module.js:434:25)
    at Object..js (module.js:464:10)
    at Module.load (module.js:353:31)
    at Function._load (module.js:311:12)
    at Module.require (module.js:359:17)
    at require (module.js:375:17)
    at Object.<anonymous> (D:\home\site\wwwroot\node_modules\mongoose\index.js:7:18)
    at Module._compile (module.js:446:26)
    at Object..js (module.js:464:10)
    at Module.load (module.js:353:31)

Error is thrown everytime Azure Web App project is made and an Express App is published. I tried with Azure Express as well as Blank nodeJs App to do it

Answer 1

Looks like it's caused by an invalid node version on Azure. Go to Azure portal, your Web App - Application settings, check WEBSITE_NODE_DEFAULT_VERSION.

Once we specify a version not available on Azure, a quite old version 0.10.40 is in use, where const is not enabled by default so that we met SyntaxError: Use of const in strict mode. See related thread for more details.

We can use 10.6.0, 8.11.1, etc. Go to https://<yourwebappname>.scm.azurewebsites.net/api/diagnostics/runtime to see all versions available.

Caveat by Clinkz

In some cases, the above solution may not work. This may be because your project includes the file iisnode.yml. If this file exists, it overrides application settings environment variable. The content of this file should be as follows :

nodeProcessCommandLine: "%SystemDrive%\Program Files (x86)\nodejs\0.10.4\node.exe"

The node version specified here takes precendence. To fix it, simply update the version, like so and deploy:

nodeProcessCommandLine: "%SystemDrive%\Program Files (x86)\nodejs\8.9.4\node.exe"

Refer to this.

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To conclude, the priority: iisnode.yml > package.json(engine)> Application settings. Application setting is recommended as it's easy to check and modify on portal.