Running Jest with npx and npm
Get introduced to dev dependencies and running packages using npx and npm.
We'll cover the following
Adding Jest as a dependency
Use npm
to install the jest
package:
$ npm install --save-dev jest@23.6.0 # 1
...
npm created a lockfile as package-lock.json. You should commit this file. # 2
+ jest@23.6.0
added 538 packages from 269 contributors in 24.446s # 3
- The
--save-dev
flag tellsnpm
, “I want to use thejest
package for development only. My project doesn’t need it at runtime.” Thejest@23.6.0
means “I want version23.6.0
of thejest
package.”- For reasons that are too involved to go into here, the information in
package.json
isn’t enough for two machines to be guaranteed to get the samenode_modules
, even if you specify exact versions for all dependencies. That’s whynpm
creates the lockfile. If you’re curious about the details, check out thenpm
docs.- The “538 packages” figure is striking, but it’s propper for Node packages: You depend on one package, which depends on several other packages, which each, in turn, depend on several more, and so on.
npm
recursively installs all of them. If you’re curious to see what all these packages are, take a peek at the freshly creatednode_modules
directory.
Try and install the package in the terminal below. You can also read the
package.json
file usingcat package.json
.
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