Merge pull request #6 from alexanderywang/isPrime

fast prime number checker

Author: johnptmcdonald

src/isPrime.js

@@ -0,0 +1,20 @@
+/**
+ * A function to test if a number is a prime number
+ * @param number - The number you want to test
+ * @return - boolean for whether or not a number is prime
+ */
+
+const isPrime = number => {
+  if (!Number.isInteger(number)) return false
+  if (number <= 1) return false
+  if (number === 2) {
+    return true;
+  }
+  if (number % 2 === 0) return false;
+  for (let i = 3; i <= parseInt(Math.sqrt(number)); i += 2) {
+    if (number % i === 0) return false;
+  }
+  return true;
+};
+
+module.exports = isPrime;

src/tests/isPrime.test.js

@@ -0,0 +1,25 @@
+const expect = require("chai").expect;
+const isPrime = require("../isPrime");
+
+describe("isPrime", () => {
+  it("returns a boolean denoting whether a number is a prime number", () => {
+    const num = 7;
+    const num2 = 24;
+    expect(isPrime(num)).to.be.true;
+    expect(isPrime(num2)).to.be.false;
+  });
+  it("returns false if a number is less than or equal to 1", () => {
+    const num = -7;
+    const num2 = 0;
+    expect(isPrime(num)).to.be.false;
+    expect(isPrime(num2)).to.be.false;
+  });
+  it("returns false if a number is not an integer", () => {
+    const num = 7.3;
+    const num2 = 31.5;
+    const num3 = 5.0
+    expect(isPrime(num)).to.be.false;
+    expect(isPrime(num2)).to.be.false;
+    expect(isPrime(num3)).to.be.true;
+  });
+});