commit lecture 2 live code

S2021/lecture2/.gitignore

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+node_modules

S2021/lecture2/async.js

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+// const sync = () => {
+//   console.log('first')
+//   console.log('second')
+// }
+
+// sync()
+
+// const expensiveOperation = () => {
+//   setTimeout(() => {
+//     console.log('i am expensive')
+//   }, 5000)
+// }
+
+// const async = () => {
+//   console.log('first')
+//   expensiveOperation()
+//   console.log('second')
+// }
+
+// async() // -> how about now?
+
+
+// setTimeout(() => {
+//   console.log('woah')
+// }, 2)
+
+// let x = 1
+// while (x < 10000000000) {
+//   x = x + 1
+// }
+// console.log(x)
+
+const expensiveOperation = () => {
+  setTimeout(() => {
+    console.log('i am expensive')
+    return 'data'
+  }, 5000)
+}
+
+const async = () => {
+  console.log('first')
+  const data = expensiveOperation()
+  console.log(`data: ${data}`)
+}
+
+async() // -> how about now?

S2021/lecture2/axios.js

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+// READ APIs
+const axios = require('axios')
+
+// DOCS can be found on https://www.npmjs.com/package/axios
+
+const data = axios.get('https://jsonplaceholder.typicode.com/todos/1')
+
+// Approach 1: using promises
+// const fetchDataPromise = () => {
+//   axios.get('https://jsonplaceholder.typicode.com/todos/1')
+//   .then(resp => {
+//     const { data } = resp
+//     console.log(data)
+//   })
+//   .catch(error => {
+//     console.log(error)
+//   })
+// }
+
+// Approach 2: still using promises + async/ await
+const fetchDataAwait = async () => {
+  const { data } = await axios.get('https://jsonplaceholder.typicode.com/todos/1')
+  console.log(data)
+}
+
+// fetchDataPromise()
+fetchDataAwait()

S2021/lecture2/hw-readFile.js

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+const csv = require('csv-parser')
+const fs = require('fs')
+
+const records = []
+
+// const appendRecord = data => {
+//   records.push(data)
+// }
+
+const printRecord = () => {
+  // console.log(records)
+}
+
+// THE WAY WE DID IN HOMEWORK
+fs.createReadStream('./PatientInfo.csv')
+  .pipe(csv())
+  .on('data', data => {
+    records.push(data)
+  })
+  .on('end', printRecord)
+
+console.log(records)

S2021/lecture2/package.json

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+{
+  "name": "lecture2",
+  "version": "1.0.0",
+  "description": "",
+  "main": "async.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "axios": "^0.21.1",
+    "csv-parse": "^4.15.0",
+    "csv-parser": "^3.0.0"
+  }
+}

S2021/lecture2/readFile.js

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+// READ FILES
+
+const fs = require('fs')
+const parse = require('csv-parse/lib/sync')
+const util = require('util')
+
+// const data = fs.readFile('./PatientInfo.csv', 'utf8', () => {})
+// console.log('hello')
+// console.log(data)
+// console.log('hello2')
+
+// Approach 1: READ FILE USING CALLBACK
+const readCallback = () => {
+  const callback = function (err, data) {
+    const records = parse(data, {
+      columns: true,
+      skip_empty_lines: true
+    })
+
+    console.log(records)
+  }
+
+  fs.readFile('./PatientInfo.csv', 'utf8', callback)
+}
+
+// Approach 2: READ FILE USING PROMISES
+const readPromise = () => {
+  // convert the function into the promise version
+  // reference: https://stackoverflow.com/questions/46867517/how-to-read-file-with-async-await-properly
+  const readFile = util.promisify(fs.readFile)
+
+  readFile('./PatientInfo.csv', 'utf8').then(data => {
+    const records = parse(data, {
+      columns: true,
+      skip_empty_lines: true
+    })
+
+    console.log(records)
+  })
+}
+
+// Approach 3: READ FILE USING PROMISES + async/ await
+const readPromiseAsync = async () => {
+  // convert the function into the promise version
+  const readFile = util.promisify(fs.readFile)
+
+  const data = await readFile('./PatientInfo.csv', 'utf8')
+
+  const records = parse(data, {
+    columns: true,
+    skip_empty_lines: true
+  })
+
+  console.log(records)
+}
+
+const readSync = () => {
+  let patientCsv = fs.readFileSync()
+  let records = parse(patientCsv, {
+    columns: true,
+    skip_empty_lines: true
+  })
+  console.log(records)
+}
+
+// readCallback()
+// readPromise()
+readPromiseAsync()

S2021/lecture2/readFileasync.js

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+const fs = require('fs')
+const parse = require('csv-parse/lib/sync')
+const util = require('util')
+
+const readPromiseAsync = async () => {
+  // convert the function into the promise version
+  const readFile = util.promisify(fs.readFile)
+
+  const data = await readFile('./PatientInfo.csv', 'utf8')
+
+  console.log(data)
+
+  const records = parse(data, {
+    columns: true,
+    skip_empty_lines: true
+  })
+
+  console.log(records)
+}
+
+readPromiseAsync()