/**

* Utility method to ensure a NgModule is only imported once in a codebase, otherwise will throw to help prevent accidental double importing

* @param parentModule Parent module name

* @param moduleName The module name

*/

export function throwIfAlreadyLoaded(parentModule: any, moduleName: string) {

if (parentModule) {

throw new Error(`${moduleName} has already been loaded. Import ${moduleName} in the AppModule only.`);

}

}

/**

* Utility method which will only fire the callback once ever

* @param fn callback to call only once

*/

export function once(fn: Function) {

let wasCalled = false;

return function wrapper() {

if (wasCalled) {

return;

}

wasCalled = true;

fn.apply(null, arguments);

};

}