Initial commit

Author: anttiai

src/throttle.js

@@ -0,0 +1,47 @@
+var throttle = function(delay, callback) {
+
+  // last time callback was executed.
+  var lastExec = 0;
+
+  // returned by setTimeout
+  var timeout;
+
+  // Clear existing timeout
+  function clearExistingTimeout() {
+    if (timeout) {
+      clearTimeout(timeout);
+    }
+  }
+
+  /*
+   * Wrap the callback inside a throttled function
+   */
+  function wrapper() {
+
+    var self = this;
+    var elapsed = Date.now() - lastExec;
+    var args = arguments;
+
+    // Execute callback function
+    function exec() {
+      lastExec = Date.now();
+      callback.apply(self, args);
+    }
+
+    clearExistingTimeout();
+
+    // Execute
+    if (elapsed > delay) {
+      exec();
+    }
+    // Schedule for a later execution
+    else {
+      timeout = setTimeout(exec, delay - elapsed);
+    }
+  }
+
+  // Return the wrapper function.
+  return wrapper;
+}
+
+module.exports = throttle;

test/throttle.js

@@ -0,0 +1,49 @@
+var assert = require('assert');
+var throttle = require('../src/throttle');
+
+function sleep(ms) {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
+describe('throttle', function() {
+
+  it('function shouldn\'t be throttled (30 function calls in 600ms)', async function() {
+    this.timeout(5000);
+    var functionCalls = 30;
+    var sleepTime = 20; // 30*20 = 600 ms
+    var expectedExecutions = 30; // Function called in every iteration
+    var executions = 0;
+
+    var f = function() {
+      executions++;
+    };
+
+    for (var i=0; i<functionCalls; i++) {
+      f();
+      await sleep(sleepTime);
+    }
+
+    assert.equal(expectedExecutions, executions);
+  });
+
+  it('function should be throttled (4 function calls in 600ms', async function() {
+    this.timeout(5000);
+    var functionCalls = 30;
+    var sleepTime = 20; // 30*20 = 600 ms
+    var throttleDelay = 200;
+    var expectedExecutions = 3 + 1; // Call functions for 600 ms with 200 ms throttle = 3 calls + one last call
+    var executions = 0;
+
+    var f = throttle(throttleDelay, function() {
+      executions++;
+    });
+
+    for (var i=0; i<functionCalls; i++) {
+      f();
+      await sleep(sleepTime);
+    }
+
+    assert.equal(expectedExecutions, executions);
+  });
+
+});