feat(useToString): new function

packages/shared/useToString/index.md

@@ -0,0 +1,18 @@
+---
+category: Utilities
+---
+
+# useToString
+
+Reactively convert a ref to string.
+
+## Usage
+
+```ts
+import { useToString } from '@vueuse/core'
+
+const number = ref(3.14)
+const str = useToString(number)
+
+str.value // '3.14'
+```

packages/shared/useToString/index.test.ts

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+import { ref } from 'vue-demi'
+import { useToString } from '.'
+
+describe('useToString', () => {
+  it('default', () => {
+    const value = ref<any>(123.345)
+    const str = useToString(value)
+
+    expect(str.value).toBe('123.345')
+
+    value.value = 'hi'
+
+    expect(str.value).toBe('hi')
+
+    value.value = { foo: 'hi' }
+
+    expect(str.value).toBe('[object Object]')
+  })
+})

packages/shared/useToString/index.ts

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+import type { ComputedRef } from 'vue-demi'
+import { computed } from 'vue-demi'
+import { resolveUnref } from '../resolveUnref'
+import type { MaybeComputedRef } from '../utils'
+
+/**
+ * Reactively convert a ref to string.
+ *
+ * @see https://vueuse.org/useToString
+ */
+export function useToString(
+  value: MaybeComputedRef<unknown>,
+): ComputedRef<string> {
+  return computed(() => `${resolveUnref(value)}`)
+}