An essential point to remember a training course is to take notes and discuss the subject with others. That's why every day I will post on dev.to the concepts and notes that I learned the day before.
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Without further ado here is a summary of my notes for today.
Numbers
In Javascript numbers are always represented as decimal
console.log(20 === 20.0) // true In Javascript numbers are represent internally by binary base
console.log(0.1 + 0.2 === 0.3) // false because of binary rounding Numbers methods
// convert string to number console.log(Number('20')) // 20 // or console.log(+'20') // 20 // parsing (extracting) number from string console.log(Number.parseInt('100px') // 100 console.log(Number.parseFloat('100.5 pixel') // 100.5 // Check if is number console.log(Number.isFinite(20)) // true console.log(Number.isFinite('20')) // false console.log(Number.isFinite('Test 20')) // false Math
// Max console.log(Math.max(5, 10, 25, 7, 2) // 25 console.log(Math.max(5, 10, '25', 7, 2) // 25 // Random between 0 and 1 console.log(Math.random()) // 0.92 // Rounding integer console.log(Math.trunc(20.5)) // 20 // Round console.log(Math.round(20.5)) // 21 // Ceil console.log(Math.ceil(20.2)) // 21 // Floor console.log(Math.floor(20.5)) // 20 // Round decimal (string decimal) console.log((20.5).toFixed(2)) // '21.50' console.log(+(20.5).toFixed(2)) // 21.50 Remainder operator
console.log(10 % 2) // 0 console.log(5 % 2) // 1 // Check if number is even console.log(6 % 2 === 0) // true console.log(5 % 2 === 0) // false // Check if number is odd console.log(6 % 2 !== 0) // false console.log(5 % 2 !== 0) // true Date and Time
// Create a date const now = new Date() const myDate = new Date('Aug 02 1999') const myLongDate = new Date('January 1, 2021') // Month is zero base (0 = January, 1 = February, ...) const dateTime = new Date(2021, 02, 28, 22, 17, 30) console.log(now) // Wed Mar 03 2021 12:47:59 GMT-0500 console.log(myDate) // Mon Aug 02 1999 00:00:00 GMT-0400 console.log(myLongDate) // Fri Jan 01 2021 00:00:00 GMT-0500 console.log(dateTime) // Sun Mar 28 2021 22:17:30 GMT-0400 Date methods
const firstDate = new Date('January 1, 2021') console.log(firstDate.getFullYear()) // 2021 console.log(firstDate.getMonth()) // 1 console.log(firstDate.getDate()) // 5 (zero base) console.log(firstDate.getDay()) // 1 console.log(firstDate.getHours()) console.log(firstDate.getMinutes()) console.log(firstDate.getSeconds()) // Set firstDate.setFullYear = 2021 // Current timestamps console.log(Date.now()) Date internationalisation
const firstDate = new Date('January 1, 2021') console.log(new Intl.DateTimeFormat('en-US').format(firstDate)) // 1/1/2021 console.log(new Intl.DateTimeFormat('fr-CA').format(firstDate)) // 2021-01-01 Format date options
const options = { hour: 'numeric', minute: 'numeric', day: 'numeric', month: 'long', year: 'numeric', weekday: 'short', } const firstDate = new Date('January 1, 2021') console.log(new Intl.DateTimeFormat('en-US', options).format(firstDate)) // Fri, January 1, 2021, 12:00 AM Get local from navigator
console.log(navigator.language) // en-US Numbers internationalisation
console.log(new Intl.NumberFormat('en-US').format(9999.95)) // 9,999.95 console.log(new Intl.NumberFormat('fr-CA').format(9999.95)) // 9 999,95 const options = { style: 'currency', currency: 'USD' // CAD for Canadian } console.log(new Intl.NumberFormat('en-US', options).format(9999.95)) // $9,999.95 Timer
// Wait 5 seconds setTimeout(() => console.log('5 sec wait'), 5000) console.log('Waiting...') // pass parameters to setTimeout setTimeout((message) => console.log(`${message}`), 5000, 'Wait is over') // Clear Timer const timer1 = setTimeout((message) => console.log(`${message}`), 5000, 'Wait is over') const condition = true if (condition) clearTimeout(timer1) // Set Interval setInterval(() => console.log('Execute every 3 sec'), 3000) 
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