var m = angular.module('hd',[])

means declaring a module called hd. Equivalent to setter, [] represents an array, and the content inside is the other modules that need to be used in the module you are declaring now. For example

var app = angular.module('app',['ionic'])

The above means that a module called app is defined, and the ionic module is injected into the app module

Also

var m = angular.module('hd')

means to get a module called hd. Equivalent to getter

angular.module('app',[]); // 声明一个module,[]里面添加该model的依赖 angular.module('app'); // 获取module

This is a declaration of a moudle.

Simply put,[]的元素为stringis the name of another NG module that depends on it.

[] contains the names of the dependent modules you need to use below ['1', '2'...] like this.