Supported force-npm option for create-react-native-app.

[metheglin]

I'd like to add --force-npm option for create-react-native-app command.
This is because I usually use yarn but it gives an error when starting react native. I added another issue for yarn for this problem.
yarnpkg/yarn#3925

As current workaround, I'd like to force npm at starting the project.
How do you think?

[ide]

Just throwing out another idea, would --package-manager=npm be a preferable interface? That way you could provide a path to a specific version of a package manager too, use ied, and so on. Not sure if it's actually something people want though.

[metheglin]

@ide
Thanks. That sounds much better.
I revised with --package-manager option. It supports specific path to run manager command.
A subtle point is the last one, if specific path which doesn't contain yarn and npm in itself is specified, this version consider it as npm as default.(so that the last one fails with test: --save-dev: unknown operand)
Please check this.

% yarn --version
0.27.5
% node index.js sample-app
Creating a new React Native app in /Users/metheglin/Documents/workspace-vagrant/rvprov-tenderloin/shared/create-react-native-app/create-react-native-app/build/sample-app.

Using package manager as yarnpkg with yarn interface.
Installing packages. This might take a couple minutes.
Installing react-native-scripts...

yarn add v0.27.5
...

% node index.js sample-app --package-manager yarn
Creating a new React Native app in /Users/metheglin/Documents/workspace-vagrant/rvprov-tenderloin/shared/create-react-native-app/create-react-native-app/build/sample-app.

Using package manager as yarn with yarn interface.
Installing packages. This might take a couple minutes.
Installing react-native-scripts...

yarn add v0.27.5
...

% node index.js sample-app --package-manager /usr/local/Cellar/yarn/0.18.1/bin/yarn
Creating a new React Native app in /Users/metheglin/Documents/workspace-vagrant/rvprov-tenderloin/shared/create-react-native-app/create-react-native-app/build/sample-app.

Using package manager as /usr/local/Cellar/yarn/0.18.1/bin/yarn with yarn interface.
Installing packages. This might take a couple minutes.
Installing react-native-scripts...

yarn add v0.18.1
...

# 
# Disabled yarn
# 
% rm -i /usr/local/bin/yarnpkg
% which yarnpkg
yarnpkg not found

% node index.js sample-app
Creating a new React Native app in /Users/metheglin/Documents/workspace-vagrant/rvprov-tenderloin/shared/create-react-native-app/create-react-native-app/build/sample-app.

Using package manager as npm with npm interface.
Installing packages. This might take a couple minutes.
Installing react-native-scripts...

sample-app@0.1.0 /Users/metheglin/Documents/workspace-vagrant/rvprov-tenderloin/shared/create-react-native-app/create-react-native-app/build/sample-app
└─┬ react-native-scripts@0.0.50
...

% node index.js sample-app --package-manager npm
Creating a new React Native app in /Users/metheglin/Documents/workspace-vagrant/rvprov-tenderloin/shared/create-react-native-app/create-react-native-app/build/sample-app.

Using package manager as npm with npm interface.
Installing packages. This might take a couple minutes.
Installing react-native-scripts...
...

% node index.js sample-app --package-manager test
Creating a new React Native app in /Users/metheglin/Documents/workspace-vagrant/rvprov-tenderloin/shared/create-react-native-app/create-react-native-app/build/sample-app.

Using package manager as test with npm interface.
Installing packages. This might take a couple minutes.
Installing react-native-scripts...

test: --save-dev: unknown operand
`test install --save-dev --save-exact react-native-scripts` failed