feat(utils): add debouncedRef function

- create a reference to the original value from the Vue instance, and only update the original after debouncing

docs/src/pages/quasar-utils/other-utils.md

@@ -291,6 +291,33 @@ runSequentialPromises([ /* ... */ ], { threadsNumber: 3 })
   })
 ```
 
+## Debounced Ref <q-badge align="top" label="v1.14+" />
+Creates a new reference to an existing value in the Vue instance that will be updated in real-time, while the original value will be updated after a debouncing period.
+
+The new value can be used as model for a control that updates frequently (eg. QInput, QSlider, QRange, ...), while the original value will only be updated after debouncing (eg. You have a search field but you only want to perform the remote search API call 300ms after the last change in the search field).
+
+``` js
+import { debouncedRef } from 'quasar'
+
+....
+data () {
+  return {
+    search: '',
+    debouncedSearch: debouncedRef(this, 'search', 500)
+  }
+},
+
+watch: {
+  debouncedSearch (newSearch, oldSearch) {
+    ...
+  }
+}
+```
+
+::: warning
+If the debounced value is an object only modify it as a whole, because it is passed by reference. If you change the value of keys inside the object the change will propagate immediatelly.
+:::
+
 ## Debounce Function
 If your App uses JavaScript to accomplish taxing tasks, a debounce function is essential to ensuring a given task doesn't fire so often that it bricks browser performance. Debouncing a function limits the rate at which the function can fire.
 

ui/dev/src/pages/form/debounced-ref.vue

@@ -0,0 +1,72 @@
+<template>
+  <div class="q-layout-padding column q-gutter-y-md">
+    <div class="q-pa-md bg-grey-3">
+      <div>original1: [{{ original1 }}]</div>
+      <input type="number" v-model.number="original1" step="1" />
+
+      <div>debounced1: [{{ debounced1.value }}]</div>
+      <input type="number" v-model.number="debounced1.value" step="1" />
+      <q-input type="number" v-model.number="debounced1.value" step="1" />
+      <q-slider v-model="debounced1.value" :step="1" />
+    </div>
+
+    <div class="q-pa-md bg-grey-3">
+      <div>original2: [{{ original2 }}]</div>
+      <input type="number" v-model.number="original2.test" step="1" />
+
+      <div>debounced2test: [{{ debounced2test.value }}]</div>
+      <input type="number" v-model.number="debounced2test.value" step="1" />
+      <q-input type="number" v-model.number="debounced2test.value" step="1" />
+      <q-slider v-model="debounced2test.value" :step="1" />
+    </div>
+
+    <div class="q-pa-md bg-grey-3">
+      <div>original3: [{{ original3 }}]</div>
+      <input type="number" v-model.number="original3.min" step="1" />
+      <input type="number" v-model.number="original3.max" step="1" />
+
+      <div>debounced3: [{{ debounced3.value }}]</div>
+      <q-range v-model="debounced3.value" drag-range :step="1" />
+    </div>
+  </div>
+</template>
+
+<script>
+import { debouncedRef } from 'quasar'
+
+export default {
+  data () {
+    return {
+      original1: 1,
+      debounced1: debouncedRef(this, 'original1', 1000),
+
+      original2: {
+        test: 2,
+        other: 3
+      },
+      debounced2test: debouncedRef(this, 'original2test', 1000),
+
+      original3: {
+        min: 10,
+        max: 40
+      },
+      debounced3: debouncedRef(this, 'original3', 1000)
+    }
+  },
+
+  computed: {
+    original2test: {
+      get () { return this.original2.test },
+      set (value) { this.original2.test = value }
+    }
+  },
+
+  beforeDestroy () {
+    console.log('beforeDestroy 1', this.original1, this.original2.test, this.original3.min, this.original3.max)
+
+    this.$nextTick(() => {
+      console.log('beforeDestroy 2', this.original1, this.original2.test, this.original3.min, this.original3.max)
+    })
+  }
+}
+</script>

ui/src/utils.js

@@ -3,6 +3,7 @@ import colors from './utils/colors.js'
 import copyToClipboard from './utils/copy-to-clipboard.js'
 import date from './utils/date.js'
 import debounce from './utils/debounce.js'
+import debouncedRef from './utils/debounced-ref.js'
 import dom from './utils/dom.js'
 import event, { noop } from './utils/event.js'
 import exportFile from './utils/export-file.js'
@@ -24,6 +25,7 @@ export {
   copyToClipboard,
   date,
   debounce,
+  debouncedRef,
   dom,
   event,
   noop,

ui/src/utils/debounced-ref.js

@@ -0,0 +1,48 @@
+export default function (vm, prop, wait = 250) {
+  const debounced = {
+    get value () {
+      const value = vm[prop]
+
+      if (value !== debounced.propValue) {
+        debounced.propValue = value
+        debounced.internalValue = value
+
+        debounced.timer !== void 0 && clearTimeout(debounced.timer)
+        debounced.timer = void 0
+      }
+
+      return debounced.internalValue
+    },
+
+    set value (value) {
+      if (debounced.internalValue === value) {
+        return
+      }
+
+      debounced.internalValue = value
+
+      debounced.timer !== void 0 && clearTimeout(debounced.timer)
+      debounced.timer = setTimeout(() => {
+        vm[prop] = value
+
+        debounced.timer = void 0
+      }, wait)
+    },
+
+    destroy () {
+      if (debounced.timer !== void 0) {
+        clearTimeout(debounced.timer)
+        debounced.timer = void 0
+
+        vm[prop] = debounced.internalValue
+      }
+    }
+  }
+
+  vm.$once('hook:beforeDestroy', debounced.destroy)
+
+  debounced.propValue = NaN
+  debounced.internalValue = NaN
+
+  return debounced
+}

ui/types/utils.d.ts

@@ -1,3 +1,5 @@
+import { LooseDictionary } from './ts-helpers'
+
 export * from './utils/date';
 export * from './utils/colors';
 export * from './utils/dom';
@@ -14,6 +16,10 @@ export function debounce<F extends (...args: any[]) => any>(
   wait?: number,
   immediate?: boolean
 ): F & { cancel(): void };
+export function debouncedRef<T extends LooseDictionary, K extends keyof T>(vm: T, prop: K, wait?: number): {
+  value: T[K],
+  destroy: () => void
+};
 export function exportFile(
   fileName: string,
   rawData: BlobPart,