js-notes.js

/*
For loop for iteration
without an array
*/

for (let i=0; i<10; i++) {
   console.log(i)
}

// 0
// 1
// 2
//...
// 9

/*
For loop for iteration
with an array
*/
const values = [ 0, 23, 56, 67, 100 ]

for (let i=0; i<values.length; i++) {
  const value = values[i]
  console.log(value)
}

/*
forEach method can be more succinct
*/

// short
values.forEach(value => console.log(value))

// shorter
values.forEach(console.log)

/*
you can only break out of loops
in for loops not forEach
*/

// works
for (let i=0; i<values.length; i++) {
  if (i > 2) {
    break
  }
  const value = values[i]
  console.log(value)
}

// still goes through each element, 
// break does nothing
values.forEach((value, index) => {
  if (i > 2) {
    break
  }
  console.log(value)
})

/*
template strings use backticks and
are good for adding in (interpolating)
values in to a string
*/


const name = 'Arjun'
const day = 'Thursday'
const number = 33.4

// good (can include line breaks directly)
`my name is ${name} and the day is ${day},
and my favorite number is ${number}`

// sucks (the '/n' means line break)
'my name is ' + name + ' and the day is ' + day + ',\nand my favorite number is ${number}'

/*
using map on an array returns an array
of the same length where each element
in the original array has been transformed
by whatever logic you want
*/

const data = [
  {
    name: 'Bethany',
    grade: 99
  },
  {
    name: 'Arjun',
    grade: 85
  },
]

// long-winded way
function makeStudentReports (data) {
  const results = []
  for(let i=0; i<data.length; i++) {
    const item = data[i]
    results.push(`${item.name}: ${item.grade}`)
  }
  return results
}

// using map
function makeStudentReports (data) {
  return data.map(item => `${item.name}: ${item.grade}`)
}