dc09.ru-old/js/init.js

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JavaScript
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function init() {
initStars()
computeAge()
}
function initStars() {
const colors = [
'#999','#9999ac','#ac9999','#acac99',
'#bbb','#bbbbcf','#cfbbbb','#cfcfbb',
'#eee','#e5e5ff','#ffe5e5','#ffffe5',
'#fff'
]
const len = colors.length
const canvas = document.querySelector('canvas#stars')
const css = getComputedStyle(canvas)
const w = canvas.width = styleValue(css.getPropertyValue('width' ))
const h = canvas.height = styleValue(css.getPropertyValue('height'))
// if CSS hasn't been loaded yet
// (w and h contains NaN)
const err = [w,h].some(n => isNaN(n))
if (err) {
setTimeout(init, 200)
return
}
const ctx = canvas.getContext('2d')
const radius = 3
const circle = 2 * Math.PI
ctx.clearRect(0, 0, w, h)
for (let star = 0; star < 200; star++) {
let color = Math.floor(Math.random() * len)
ctx.fillStyle = colors[color]
ctx.beginPath()
ctx.arc(
Math.round(Math.random() * w),
Math.round(Math.random() * h),
radius, 0, circle, false
)
ctx.fill()
}
}
function computeAge() {
const birthday = new Date(2009, 7, 13, 12, 30)
const timedelta = Date.now() - birthday.getTime()
/*
The line below is equivalent to:
const age = timedelta / 1000 / 60 / 60 / 24 / 365.25
where:
1000: convert milliseconds -> seconds
60: secs -> minutes
60: minutes -> hours
24: hours -> days
365.25: average count of days in a year:
(366 + (365 * 3)) / 4 = 365.25
*/
const age = timedelta / (1000 * 60 * 60 * 24 * 365.25)
document.getElementById('age-js').textContent = Math.floor(age)
}