Use custom throttle function

package.json

@@ -30,7 +30,6 @@
     "grid-index": "^1.0.0",
     "jsonlint-lines-primitives": "~1.6.0",
     "lodash.isequal": "^3.0.4",
-    "lodash.throttle": "^4.1.1",
     "mapbox-gl-supported": "^1.2.0",
     "minimist": "0.0.8",
     "package-json-versionify": "^1.0.2",

src/ui/hash.js

@@ -2,7 +2,7 @@
 
 const util = require('../util/util');
 const window = require('../util/window');
-const throttle = require('lodash.throttle');
+const throttle = require('../util/throttle');
 
 import type Map from './map';
 

src/util/throttle.js

@@ -0,0 +1,35 @@
+// @flow
+
+/**
+ * Throttle the given function to run at most every `period` milliseconds.
+ */
+module.exports = function(unthrottledFunction: () => void, period: number): () => void {
+
+    // The next time (unix epoch) that the function is allowed to execute
+    let nextTime = 0;
+
+    // `true` if there is a pending "setTimeout" operation that'll invoke the
+    // function at a later time. `false` if there is not.
+    let pending = false;
+
+    let throttledFunction = () => {
+        const time = Date.now();
+
+        if (nextTime <= time && !pending) {
+            nextTime = time + period;
+            unthrottledFunction();
+        } else if (!pending) {
+            pending = true;
+            setTimeout(_throttledFunction, nextTime - time);
+        }
+    };
+
+    // This callback to `setTimeout` is written outside `throttledFunction` to
+    // reduce the number of closures created.
+    let _throttledFunction = () => {
+        pending = false;
+        throttledFunction();
+    };
+
+    return throttledFunction;
+};

src/util/util.js

@@ -457,3 +457,29 @@ exports.parseCacheControl = function(cacheControl: string): Object {
 
     return header;
 };
+
+/**
+ * Throttle the given function to run at most every `time` milliseconds.
+ */
+exports.throttle = function(fn: () => void, time: number): () => number {
+    let pending = false;
+    let timerId = 0;
+
+    const later = () => {
+        timerId = 0;
+        if (pending) {
+            fn();
+            pending = false;
+        }
+    };
+
+    return () => {
+        if (timerId) {
+            pending = true;
+        } else {
+            fn();
+            timerId = setTimeout(later, time);
+        }
+        return timerId;
+    };
+};

test/unit/util/throttle.test.js

@@ -0,0 +1,49 @@
+'use strict';
+// @flow
+
+const test = require('mapbox-gl-js-test').test;
+const throttle = require('../../../src/util/throttle');
+
+test('throttle', (t) => {
+
+    t.test('does not execute unthrottled function unless throttled function is invoked', (t) => {
+        let executionCount = 0;
+        let throttledFunction = throttle(() => executionCount++, 0);
+        t.equal(executionCount, 0);
+        t.end();
+    });
+
+    t.test('executes unthrottled function immediately when period is 0', (t) => {
+        let executionCount = 0;
+        let throttledFunction = throttle(() => executionCount++, 0);
+        throttledFunction();
+        throttledFunction();
+        throttledFunction();
+        t.equal(executionCount, 3);
+        t.end();
+    });
+
+    t.test('executes unthrottled function once when period is > 0', (t) => {
+        let executionCount = 0;
+        let throttledFunction = throttle(() => executionCount++, 5);
+        throttledFunction();
+        throttledFunction();
+        throttledFunction();
+        t.equal(executionCount, 1);
+        t.end();
+    });
+
+    t.test('queues exactly one execution of unthrottled function when period is > 0', (t) => {
+        let executionCount = 0;
+        let throttledFunction = throttle(() => executionCount++, 5);
+        throttledFunction();
+        throttledFunction();
+        throttledFunction();
+        setTimeout(() => {
+            t.equal(executionCount, 2);
+            t.end();
+        }, 10);
+    });
+
+    t.end();
+});

yarn.lock

@@ -6189,10 +6189,6 @@ lodash.templatesettings@^3.0.0:
     lodash._reinterpolate "^3.0.0"
     lodash.escape "^3.0.0"
 
-lodash.throttle@^4.1.1:
-  version "4.1.1"
-  resolved "https://registry.yarnpkg.com/lodash.throttle/-/lodash.throttle-4.1.1.tgz#c23e91b710242ac70c37f1e1cda9274cc39bf2f4"
-
 lodash.toplainobject@^3.0.0:
   version "3.0.0"
   resolved "https://registry.yarnpkg.com/lodash.toplainobject/-/lodash.toplainobject-3.0.0.tgz#28790ad942d293d78aa663a07ecf7f52ca04198d"