Counting months from zero
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Posted on Many programming languages start counting months one number before we would. It’s like saying January is “month zero” and December is “month eleven”.
const months = [
"January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November", "December"
]
// `.length` tells us how many months there are in a year.
months.length // ⇒ 12
// Counting in an array start at 0, so the months are numbered from 0 to 11.
// A year still has 12 months, but we need to shift their index down by 1.
// While January is the 1st month for us, it’s the 0th element in the array.
months[0] // ⇒ "January"
// The index of December is also one less than what we would say.
months[11] // ⇒ "December"
// The month at the index 12 would be the 13th month, which does not exist.
months[12] // ⇒ undefined
const iPhoneReleaseDate = new Date('June 29, 2007');
iPhoneReleaseDate.getMonth()
// ⇒ 5 (because June is the 6th month)const months = [
"January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November", "December"
]
// `.length` tells us how many months there are in a year.
months.length // ⇒ 12
// Counting in an array start at 0, so the months are numbered from 0 to 11.
// A year still has 12 months, but we need to shift their index down by 1.
// While January is the 1st month for us, it’s the 0th element in the array.
months[0] // ⇒ "January"
// The index of December is also one less than what we would say.
months[11] // ⇒ "December"
// The month at the index 12 would be the 13th month, which does not exist.
months[12] // ⇒ undefined
const iPhoneReleaseDate = new Date('June 29, 2007');
iPhoneReleaseDate.getMonth()
// ⇒ 5 (because June is the 6th month)const months = [
"January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November", "December"
]
// `.length` tells us how many months there are in a year.
months.length // ⇒ 12
// Counting in an array start at 0, so the months are numbered from 0 to 11.
// A year still has 12 months, but we need to shift their index down by 1.
// While January is the 1st month for us, it’s the 0th element in the array.
months[0] // ⇒ "January"
// The index of December is also one less than what we would say.
months[11] // ⇒ "December"
// The month at the index 12 would be the 13th month, which does not exist.
months[12] // ⇒ undefined
const iPhoneReleaseDate = new Date('June 29, 2007');
iPhoneReleaseDate.getMonth()
// ⇒ 5 (because June is the 6th month)const months = [
"January", "February", "March", "April", "May", "June",
"July", "August", "September", "October", "November", "December"
]
// `.length` tells us how many months there are in a year.
months.length // ⇒ 12
// Counting in an array start at 0, so the months are numbered from 0 to 11.
// A year still has 12 months, but we need to shift their index down by 1.
// While January is the 1st month for us, it’s the 0th element in the array.
months[0] // ⇒ "January"
// The index of December is also one less than what we would say.
months[11] // ⇒ "December"
// The month at the index 12 would be the 13th month, which does not exist.
months[12] // ⇒ undefined
const iPhoneReleaseDate = new Date('June 29, 2007');
iPhoneReleaseDate.getMonth()
// ⇒ 5 (because June is the 6th month)