SyntaxError: Invalid assignment

[pranavtheway]

I encountered the SyntaxError: Invalid assignment for the code which is javascript promise.

Last time when I faced and gulp util deprecation issue, i upgraded my gulp minify to gulp-minify@es5 and now when I have implemented the javascript promise functionality, i observe the mentioned Syntax error. during minification.

Below is the dependecies:

 "gulp": "^3.9.1",
    "gulp-clean": "^0.3.2",
    "gulp-clean-css": "^3.9.2",
    "gulp-copy": "^1.0.1",
    "gulp-gzip": "^1.4.0",
    "gulp-htmlmin": "^4.0.0",
    "gulp-minify": "0.0.15",
    "gulp-rename": "^1.2.2"

Please suggest, what needs to be done here.