Extract helper

Author: kurkle

src/core/core.controller.js

@@ -11,6 +11,7 @@ import {each, callback as callCallback, uid, valueOrDefault, _elementsEqual} fro
 import {clearCanvas, clipArea, unclipArea, _isPointInArea} from '../helpers/helpers.canvas';
 // @ts-ignore
 import {version} from '../../package.json';
+import {debounce} from '../helpers/helpers.extras';
 
 /**
  * @typedef { import("../platform/platform.base").ChartEvent } ChartEvent
@@ -122,7 +123,7 @@ class Chart {
     this.attached = false;
     this._animationsDisabled = undefined;
     this.$context = undefined;
-    this._resizeTimer = undefined;
+    this._doResize = debounce(() => this.update('resize'), options.resizeDelay || 0);
 
     // Add the chart instance to the global namespace
     instances[me.id] = me;
@@ -243,14 +244,9 @@ class Chart {
     callCallback(options.onResize, [newSize], me);
 
     if (me.attached) {
-      const delay = options.resizeDelay || 0;
-      const resizeUpdate = () => me.update('resize');
-      if (delay) {
-        clearTimeout(me._resizeTimer);
-        me._resizeTimer = setTimeout(resizeUpdate, delay);
+      if (me._doResize()) {
+        // The resize update is delayed, only draw without updating.
         me.render();
-      } else {
-        resizeUpdate();
       }
     }
   }

src/helpers/helpers.extras.js

@@ -40,6 +40,25 @@ export function throttled(fn, thisArg, updateFn) {
   };
 }
 
+/**
+ * Debounces calling `fn` for `delay` ms
+ * @param {function} fn - Function to call. No arguments are passed.
+ * @param {number} delay - Delay in ms. 0 = immediate invocation.
+ * @returns {function}
+ */
+export function debounce(fn, delay) {
+  let timeout;
+  return function() {
+    if (delay) {
+      clearTimeout(timeout);
+      timeout = setTimeout(fn, delay);
+    } else {
+      fn();
+    }
+    return delay;
+  };
+}
+
 
 /**
  * Converts 'start' to 'left', 'end' to 'right' and others to 'center'