Initial migration on TS

src/index.ts

@@ -0,0 +1,20 @@
+import {debug, getInput, setOutput, setFailed} from '@actions/core'
+import {ensureYarnIsInstalled} from './yarn'
+import {run} from './run'
+
+const main = async () => {
+  await ensureYarnIsInstalled()
+
+  const cmd: string = getInput('cmd', {required: true})
+
+  try {
+    debug(`Running "${cmd}" command`)
+
+    await run(cmd)
+    setOutput(cmd, 'Done')
+  } catch (error) {
+    if (error instanceof Error) setFailed(error.message)
+  }
+}
+
+main()

src/run.ts

@@ -0,0 +1,5 @@
+import {exec} from '@actions/exec'
+
+export const run = async (cmd: string) => {
+  await exec('yarn', [cmd])
+}

src/yarn.ts

@@ -0,0 +1,18 @@
+import {debug} from '@actions/core'
+import {exec, getExecOutput} from '@actions/exec'
+import {which} from '@actions/io'
+
+export const ensureYarnIsInstalled = async () => {
+  try {
+    await which('yarn', true)
+  } catch (e) {
+    await exec('npm install --global yarn')
+  }
+
+  const [{stdout: yarnVersion}, {stdout: nodeVersion}] = await Promise.all([
+    getExecOutput('yarn', ['--version'], {silent: true}),
+    getExecOutput('node', ['--version'], {silent: true})
+  ])
+  debug(`Node ${nodeVersion.trim()} detected`)
+  debug(`Yarn v${yarnVersion.trim()} detected`)
+}