Repository: sveltejs/svelte (JavaScript) — Refactoring

Issue:
<input type=range bind:value> duplicates handlers unnecessarily
With [this markup](https://svelte.technology/repl?version=2.4.4&gist=cdf74219bd9a8a06d6af6a9d9cf9d888)...

```html
<input type=range bind:value>
```

...Svelte could generate leaner code:

```diff
function create_main_fragment(component, ctx) {
  var input;

  function input_input_handler() {
    component.set({ value: toNumber(input.value) });
  }

-  function input_change_handler() {
-    component.set({ value: toNumber(input.value) });
-  }
-
  return {
    c: function create() {
      input = createElement("input");
      addListener(input, "input", input_input_handler);
-      addListener(input, "change", input_change_handler);
+      addListener(input, "change", input_input_handler);
      setAttribute(input, "type", "range");
    },

    m: function mount(target, anchor) {
      insertNode(input, target, anchor);

      input.value = ctx.value;
    },

    p: function update(changed, ctx) {
      input.value = ctx.value;
      input.value = ctx.value;
    },

    u: function unmount() {
      detachNode(input);
    },

    d: function destroy() {
      removeListener(input, "input", input_input_handler);
-      removeListener(input, "change", input_change_handler);
+      removeListener(input, "change", input_input_handler);
    }
  };
}
```


Discussion:

Resolving patch:
diff --git a/src/compile/nodes/Element.ts b/src/compile/nodes/Element.ts
--- a/src/compile/nodes/Element.ts
+++ b/src/compile/nodes/Element.ts
@@ -988,13 +988,18 @@ const events = [
 		eventNames: ['input'],
 		filter: (node: Element, name: string) =>
 			node.name === 'textarea' ||
-			node.name === 'input' && !/radio|checkbox/.test(node.getStaticAttributeValue('type'))
+			node.name === 'input' && !/radio|checkbox|range/.test(node.getStaticAttributeValue('type'))
 	},
 	{
 		eventNames: ['change'],
 		filter: (node: Element, name: string) =>
 			node.name === 'select' ||
-			node.name === 'input' && /radio|checkbox|range/.test(node.getStaticAttributeValue('type'))
+			node.name === 'input' && /radio|checkbox/.test(node.getStaticAttributeValue('type'))
+	},
+	{
+		eventNames: ['change', 'input'],
+		filter: (node: Element, name: string) =>
+			node.name === 'input' && node.getStaticAttributeValue('type') === 'range'
 	},
 
 	{


Test patch:
diff --git a/test/js/samples/input-range/expected-bundle.js b/test/js/samples/input-range/expected-bundle.js
new file mode 100644
--- /dev/null
+++ b/test/js/samples/input-range/expected-bundle.js
@@ -0,0 +1,198 @@
+function noop() {}
+
+function assign(tar, src) {
+	for (var k in src) tar[k] = src[k];
+	return tar;
+}
+
+function insertNode(node, target, anchor) {
+	target.insertBefore(node, anchor);
+}
+
+function detachNode(node) {
+	node.parentNode.removeChild(node);
+}
+
+function createElement(name) {
+	return document.createElement(name);
+}
+
+function addListener(node, event, handler) {
+	node.addEventListener(event, handler, false);
+}
+
+function removeListener(node, event, handler) {
+	node.removeEventListener(event, handler, false);
+}
+
+function setAttribute(node, attribute, value) {
+	node.setAttribute(attribute, value);
+}
+
+function toNumber(value) {
+	return value === '' ? undefined : +value;
+}
+
+function blankObject() {
+	return Object.create(null);
+}
+
+function destroy(detach) {
+	this.destroy = noop;
+	this.fire('destroy');
+	this.set = noop;
+
+	this._fragment.d(detach !== false);
+	this._fragment = null;
+	this._state = {};
+}
+
+function _differs(a, b) {
+	return a != a ? b == b : a !== b || ((a && typeof a === 'object') || typeof a === 'function');
+}
+
+function fire(eventName, data) {
+	var handlers =
+		eventName in this._handlers && this._handlers[eventName].slice();
+	if (!handlers) return;
+
+	for (var i = 0; i < handlers.length; i += 1) {
+		var handler = handlers[i];
+
+		if (!handler.__calling) {
+			handler.__calling = true;
+			handler.call(this, data);
+			handler.__calling = false;
+		}
+	}
+}
+
+function get() {
+	return this._state;
+}
+
+function init(component, options) {
+	component._handlers = blankObject();
+	component._bind = options._bind;
+
+	component.options = options;
+	component.root = options.root || component;
+	component.store = component.root.store || options.store;
+}
+
+function on(eventName, handler) {
+	var handlers = this._handlers[eventName] || (this._handlers[eventName] = []);
+	handlers.push(handler);
+
+	return {
+		cancel: function() {
+			var index = handlers.indexOf(handler);
+			if (~index) handlers.splice(index, 1);
+		}
+	};
+}
+
+function set(newState) {
+	this._set(assign({}, newState));
+	if (this.root._lock) return;
+	this.root._lock = true;
+	callAll(this.root._beforecreate);
+	callAll(this.root._oncreate);
+	callAll(this.root._aftercreate);
+	this.root._lock = false;
+}
+
+function _set(newState) {
+	var oldState = this._state,
+		changed = {},
+		dirty = false;
+
+	for (var key in newState) {
+		if (this._differs(newState[key], oldState[key])) changed[key] = dirty = true;
+	}
+	if (!dirty) return;
+
+	this._state = assign(assign({}, oldState), newState);
+	this._recompute(changed, this._state);
+	if (this._bind) this._bind(changed, this._state);
+
+	if (this._fragment) {
+		this.fire("state", { changed: changed, current: this._state, previous: oldState });
+		this._fragment.p(changed, this._state);
+		this.fire("update", { changed: changed, current: this._state, previous: oldState });
+	}
+}
+
+function callAll(fns) {
+	while (fns && fns.length) fns.shift()();
+}
+
+function _mount(target, anchor) {
+	this._fragment[this._fragment.i ? 'i' : 'm'](target, anchor || null);
+}
+
+var proto = {
+	destroy,
+	get,
+	fire,
+	on,
+	set,
+	_recompute: noop,
+	_set,
+	_mount,
+	_differs
+};
+
+/* generated by Svelte vX.Y.Z */
+
+function create_main_fragment(component, ctx) {
+	var input;
+
+	function input_change_input_handler() {
+		component.set({ value: toNumber(input.value) });
+	}
+
+	return {
+		c() {
+			input = createElement("input");
+			addListener(input, "change", input_change_input_handler);
+			addListener(input, "input", input_change_input_handler);
+			setAttribute(input, "type", "range");
+		},
+
+		m(target, anchor) {
+			insertNode(input, target, anchor);
+
+			input.value = ctx.value;
+		},
+
+		p(changed, ctx) {
+			input.value = ctx.value;
+		},
+
+		d(detach) {
+			if (detach) {
+				detachNode(input);
+			}
+
+			removeListener(input, "change", input_change_input_handler);
+			removeListener(input, "input", input_change_input_handler);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._state = assign({}, options.data);
+
+	this._fragment = create_main_fragment(this, this._state);
+
+	if (options.target) {
+		this._fragment.c();
+		this._mount(options.target, options.anchor);
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+
+export default SvelteComponent;
diff --git a/test/js/samples/input-range/expected.js b/test/js/samples/input-range/expected.js
new file mode 100644
--- /dev/null
+++ b/test/js/samples/input-range/expected.js
@@ -0,0 +1,53 @@
+/* generated by Svelte vX.Y.Z */
+import { addListener, assign, createElement, detachNode, init, insertNode, proto, removeListener, setAttribute, toNumber } from "svelte/shared.js";
+
+function create_main_fragment(component, ctx) {
+	var input;
+
+	function input_change_input_handler() {
+		component.set({ value: toNumber(input.value) });
+	}
+
+	return {
+		c() {
+			input = createElement("input");
+			addListener(input, "change", input_change_input_handler);
+			addListener(input, "input", input_change_input_handler);
+			setAttribute(input, "type", "range");
+		},
+
+		m(target, anchor) {
+			insertNode(input, target, anchor);
+
+			input.value = ctx.value;
+		},
+
+		p(changed, ctx) {
+			input.value = ctx.value;
+		},
+
+		d(detach) {
+			if (detach) {
+				detachNode(input);
+			}
+
+			removeListener(input, "change", input_change_input_handler);
+			removeListener(input, "input", input_change_input_handler);
+		}
+	};
+}
+
+function SvelteComponent(options) {
+	init(this, options);
+	this._state = assign({}, options.data);
+
+	this._fragment = create_main_fragment(this, this._state);
+
+	if (options.target) {
+		this._fragment.c();
+		this._mount(options.target, options.anchor);
+	}
+}
+
+assign(SvelteComponent.prototype, proto);
+export default SvelteComponent;
\ No newline at end of file
diff --git a/test/js/samples/input-range/input.html b/test/js/samples/input-range/input.html
new file mode 100644
--- /dev/null
+++ b/test/js/samples/input-range/input.html
@@ -0,0 +1 @@
+<input type=range bind:value>
\ No newline at end of file