const n1 =2;
const n2 =9;
//sum
let sum_n = n1 +n2 +15; // 26
//rest of division with 3
let rest3 = sum_n %3; // 2
document.write('Sum (n1+n2+15) = '+sum_n+'<br>Rest of this sum divided by 3 is: '+rest3);
Numeric strings (numbers added between quotes) cannot be used to perform correctly mathematical operations.
JavaScript uses the + operator for both addition and concatenation.
Numbers are added. Strings are concatenated
let n1 ='21';
let n2 =9;
//sum
let sum_n = n1 +n2; //219
document.write("Sum ('21'+ 9) ="+sum_n);
Before performing mathematical operations with numeric strings, they must be converted to Number.
The simplest way to convert a numeric string to Number is by: multiplying the string by 1, or with the Number() function.
let n1 ='21';
let n2 =9;
n1 = n1*1; //converts to number
let sum_n = n1 +n2; //30
document.write('Sum (21+9) = '+sum_n);
let n1 ='21';
let n2 =9;
n1 = Number(n1); //converts to number
let sum_n = n1 +n2; //30
document.write('Sum of (21+9) = '+sum_n);
Numbers without decimal are considered Integer, and the decimal numbers are considered Float.
The negative numbers are added with the minus sign (-).
Number object has some methods for numbers.
Number.isInteger(nr) - returns True if 'nr' is an Integer, otherwise, False.var n1 = 90; var n2 = -25; var n3 = 90.23; var n4 ='23'; console.log(Number.isInteger(n1)); // true console.log(Number.isInteger(n2)); // true console.log(Number.isInteger(n3)); // false console.log(Number.isInteger(n4)); // false
Number(sn) - converts a numeric string 'sn' to number. returns NaN (Not a Number) if the string is not numeric.var n1 ='57.98'; var n2 ='23 str'; console.log(Number(n1)); // 57.98 console.log(Number(n2)); // NaN
parseFloat(sn) - parses an argument and returns a floating point number.
var nr ='13.56';
nr = parseFloat(nr); //number 13.56
var sum_n = nr +8.2;
document.write('- Suma: nr +8 = '+sum_n); //21.759999999999998
parseInt(sn) - parses a string argument and returns a string with an integer number.var n1 ='25.89'; var n2 ='-34.8 23'; console.log(parseInt(n1)); // 25 console.log(parseInt(n2)); // -34
nr.toFixed(d) - returns a string representing the given number using fixed-point notation, with the specified number of decimals 'd'.var n1 = 92; var n2 = -25.5689; var n3 = 90.2378; console.log(n1.toFixed(2)); // 92.00 console.log(n2.toFixed(1)); // -25.6 console.log(n3.toFixed(2)); // 90.24
nr.toPrecision(n) - returns a string with the number from 'nr', having:var n1 = 24; var n2 = -3.23; var n3 = 0.46; console.log(n1.toPrecision(3)); // 24.0 console.log(n2.toFixed(1)); // -3.2 console.log(n3.toFixed(3)); // 0.460
nr.toString() - returns a string with the number from 'nr'.var n1 = 12.5; var sum_n = n1.toString() +3; var ex2 = (12 + 9).toString(); console.log(sum_n); // 12.53 console.log(ex2); // 21
Number() applied with the Date object returns the number of milliseconds since 1.1.1970 till the time from the Date object.
var dt1 = new Date('2018-07-15');
var dt2 = new Date('2018-07-15 11:13:00');
console.log(Number(dt1)); // 1531612800000
console.log(Number(dt2)); // 1531642380000
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