Added monte carlo javascript example (#175)

Author: xam4lor

chapters/monte_carlo/code/js/monte_carlo.js

@@ -0,0 +1,29 @@
+// submitted by xam4lor
+function inCircle(xPos, yPos) {
+  // Setting radius to 1 for unit circle
+  let radius = 1;
+  return xPos * xPos + yPos * yPos < radius * radius;
+}
+
+function monteCarlo(n) {
+  let piCount = 0;
+
+  for (let i = 0; i < n; i++) {
+    const pointX = Math.random();
+    const pointY = Math.random();
+
+    if (inCircle(pointX, pointY)) {
+      piCount++;
+    }
+  }
+
+  // This is using a quarter of the unit sphere in a 1x1 box.
+  // The formula is pi = (boxLength^2 / radius^2) * (piCount / n), but we
+  // are only using the upper quadrant and the unit circle, so we can use
+  // 4*piCount/n instead
+  // piEstimate = 4*piCount/n
+  const piEstimate = 4 * piCount / n;
+  console.log('Percent error is: %s%', 100 * (Math.PI - piEstimate) / Math.PI);
+}
+
+monteCarlo(100000000);

chapters/monte_carlo/monte_carlo.md

@@ -41,6 +41,8 @@ each point is tested to see whether it's in the circle or not:
 [import:2-7, lang:"julia"](code/julia/monte_carlo.jl)
 {% sample lang="c" %}
 [import:7-9, lang:"c_cpp"](code/c/monte_carlo.c)
+{% sample lang="js" %}
+[import:2-6, lang:"js"](code/js/monte_carlo.js)
 {% sample lang="hs" %}
 [import:7-7, lang:"haskell"](code/haskell/monteCarlo.hs)
 {% sample lang="rs" %}
@@ -86,6 +88,9 @@ Feel free to submit your version via pull request, and thanks for reading!
 {% sample lang="c" %}
 ### C
 [import, lang:"c_cpp"](code/c/monte_carlo.c)
+{% sample lang="js" %}
+### Javascript
+[import, lang:"js"](code/js/monte_carlo.js)
 {% sample lang="hs" %}
 ### Haskell
 [import, lang:"haskell"](code/haskell/monteCarlo.hs)