* MyMath.js

function MyMath() {}

MyMath.abs = function(x) {
    if (x < 0) {return -x;}
    else return x;
}

MyMath.isPrime = function(/* int */n) {
    if (n < 2) return false;
    if (n === 2|| n===3) {
	return true;
    }
    // 6x 6x+1 6x+2 6x+3 6x+4 6x+5
    // 6x+2 => 2(3x+1)
    // 6x+3 => 3(2x+1)
    // 6x+4 => 2(3x+2)
    if (n % 6 !== 1 && n % 6 !== 5) {
	return false;
    }
    for (var x = 5; x * x <= n; x += 6) {
	if (n % x === 0 || n % (x+2) === 0) {
	    return false;
	}
    }
    return true;
}

MyMath.sqrt = function(/* Number */c) {
    if (c < 0) return NaN;
    var err = 1e-15;
    var t = c;
    while (MyMath.abs(t- c/t) > err * t) {
	t = (c/t + t) / 2.0;
    }
    return t;
}

// hypotenuse of a right triangle
MyMath.hypotenuse = function(/* double */ a, /* double */b) /* double */ {
    return MyMath.sqrt(a*a + b*b);
}

// Harmonic number
MyMath.H = function(/* int */ N) {
    var sum = 0.0;
    for (var i = 1; i <= N; i++) {
	sum += 1.0 / i;
    }
    return sum;
}

module.exports = MyMath;

* index.js

const MyMath = require('./MyMath');

for (var i = 0; i < 100; i++) {
    if (MyMath.isPrime(i)) {
	console.log("Math.sqrt("+i+")=" + MyMath.sqrt(i));
    }
}

console.log( MyMath.hypotenuse(3, 4) );

console.log( MyMath.H(1000) );

node index.js

Math.sqrt(2)=1.414213562373095

Math.sqrt(3)=1.7320508075688772

Math.sqrt(5)=2.23606797749979

Math.sqrt(7)=2.6457513110645907

Math.sqrt(11)=3.3166247903554

Math.sqrt(13)=3.6055512754639905

Math.sqrt(17)=4.123105625617661

Math.sqrt(19)=4.358898943540673

Math.sqrt(23)=4.795831523312719

Math.sqrt(29)=5.385164807134505

Math.sqrt(31)=5.567764362830022

Math.sqrt(37)=6.08276253029822

Math.sqrt(41)=6.4031242374328485

Math.sqrt(43)=6.557438524302

Math.sqrt(47)=6.855654600401045

Math.sqrt(53)=7.280109889280518

Math.sqrt(59)=7.681145747868609

Math.sqrt(61)=7.810249675906654

Math.sqrt(67)=8.18535277187245

Math.sqrt(71)=8.426149773176359

Math.sqrt(73)=8.544003745317532

Math.sqrt(79)=8.888194417315589

Math.sqrt(83)=9.1104335791443

Math.sqrt(89)=9.433981132056605

Math.sqrt(97)=9.848857801796104

5

7.485470860550343