`Vue` allows for you to specify a default `prop` value and `type` directly, by making props an object (see: https://vuejs.org/guide/components.html#Prop-Validation):

    props: {
      year: {
        default: 2016,
        type: Number
      }
    }

If the wrong type is passed then it throws an error and logs it in the console, here&#39;s the fiddle:

https://jsfiddle.net/cexbqe2q/

This is an old question, but regarding the second part of the question - how can you check if the user set/didn&#39;t set a prop?

Inspecting `this` within the component, we have `this.$options.propsData`. If the prop is present here, the user has explicitly set it; default values aren&#39;t shown.

This is useful in cases where you can&#39;t really compare your value to its default, e.g. if the prop is a function.

Also something important to add here, in order to set default values for arrays and objects we must use the default function for props:

    propE: {
          type: Object,
          // Object or array defaults must be returned from
          // a factory function
          default: function () {
            return { message: &#39;hello&#39; }
          }
        },

Worth mentioning, that you also can add a custom validator function to every prop like this, to ensure the passed value matches your components specific requirements:

```js
props: {
  year: {
    type: Number,
    required: true
    validator (value) {
      return value &gt; 2015
    }
  }
}
```

I am using android.support.design.widget.BottomNavigationView from design support library version 25

    compile &#39;com.android.support:design:25.0.0&#39;

    &lt;android.support.design.widget.BottomNavigationView
            android:id=&quot;@+id/bottomBar&quot;
            android:layout_width=&quot;match_parent&quot;
            android:layout_height=&quot;wrap_content&quot;
            android:layout_alignParentBottom=&quot;true&quot;
            android:layout_gravity=&quot;center&quot;
            app:itemBackground=&quot;@color/colorPrimary&quot;
            app:menu=&quot;@menu/bottom_navigation_main&quot;
            android:forceHasOverlappingRendering=&quot;true&quot;/&gt;

When there are only three actions in @menu/bottom_navigation_main, it displays both icons and text labels at all times.

What is the way to display both icons and text labels at all the time when there are more than three actions.


BottomNavigationView display both icons and text labels at all times

I am using React and Redux and have action types specified as interfaces, so that my reducers can take advantage of tagged union types for improved type safety.

So, I have type declarations that look like this:

    interface AddTodoAction {
        type: &quot;ADD_TODO&quot;,
        text: string
    };

    interface DeleteTodoAction {
        type: &quot;DELETE_TODO&quot;,
        id: number
    }

    type TodoAction = AddTodoAction | DeleteTodoAction

I&#39;d like to make helper functions that create these actions, and I tend to use arrow functions for this. If I write this:

    export const addTodo1 = (text: string) =&gt; ({
        type: &quot;ADD_TODO&quot;,
        text
    });

The compiler can&#39;t provide any help in making sure this is a valid `AddTodoAction` because the return type isn&#39;t specified explicitly. I can specify the return type explicitly by doing this:

    export const addTodo2: (text: string) =&gt; AddTodoAction = (text: string) =&gt; ({
        type: &quot;ADD_TODO&quot;,
        text
    })

But this requires specifying my function arguments twice, so it&#39;s verbose and harder to read.

Is there a way I can specify the return type explicitly when using arrow notation?

I&#39;ve thought of trying this:

    export const addTodo3 = (text: string) =&gt; &lt;AddTodoAction&gt;({
        type: &quot;ADD_TODO&quot;,
        text
    })

In this case, the compiler now infers the return type as `AddTodoAction` but it&#39;s doesn&#39;t validate that the object I&#39;m returning has all of the appropriate fields.

I could solve this by switching to a different function syntax:

    export const addTodo4 = function(text: string): AddTodoAction {
        return {
            type: &quot;ADD_TODO&quot;,
            text
        }
    }

    export function addTodo5(text: string): AddTodoAction {
        return {
            type: &quot;ADD_TODO&quot;,
            text
        }
    }

Either of these methods will cause the compiler to use the correct return type and enforce that I have set all fields appropriately, but they are also more verbose and they change the way &#39;`this`&#39; is handled in a function (which may not be an issue, I suppose.)

Is there any advice about the best way to do this?

Specify return type in TypeScript arrow function

**1.** How can I set the default value for a component prop in Vue 2? For example, there is a simple `movies` component that can be used in this way:

    &lt;movies year=&quot;2016&quot;&gt;&lt;movies&gt;



    Vue.component(&#39;movies&#39;, {
        props: [&#39;year&#39;],
    
        template: &#39;#movies-template&#39;,
        ...
    }

But, if a user doesn&#39;t specify the `year`:

    &lt;movies&gt;&lt;/movies&gt;

then the component will take some default value for the `year` prop.

**2.** Also, what is the best way to check if a user did not set the prop? Is this a good way:

    if (this.year != null) {
        // do something
    }

or maybe this:

    if (!this.year) {
        // do something
    }
**?**

Default values for Vue component props &amp; how to check if a user did not set the prop?

1. How can I set the default value for a component prop in Vue 2? For example, there is a simple <code>movies</code> component that can be used in this way:
<pre><code class="hljs language-php">&#x3C;movies year="2016">&#x3C;movies>



Vue.component('movies', {
 props: ['year'],

 template: '#movies-template',
 ...
}
</code></pre>
But, if a user doesn't specify the <code>year</code>:
<pre><code class="hljs language-php-template">&#x3C;movies>&#x3C;/movies>
</code></pre>
then the component will take some default value for the <code>year</code> prop.
2. Also, what is the best way to check if a user did not set the prop? Is this a good way:
<pre><code class="hljs language-kotlin">if (this.year != null) {
 // do something
}
</code></pre>
or maybe this:
<pre><code class="hljs language-kotlin">if (!this.year) {
 // do something
}
</code></pre>
?

I am trying to set query params with [Vue-router][1] when changing input fields, I don&#39;t want to navigate to some other page but just want to modify url query params on the same page, I am doing like this:

    this.$router.replace({ query: { q1: &quot;q1&quot; } })

But this also refreshes the page and sets the y position to 0, ie scrolls to the top of the page. Is this the correct way to set the URL query params or is there a better way to do it.


----------
Edited:

Here is my router code:

    export default new Router({
      mode: &#39;history&#39;,
      scrollBehavior: (to, from, savedPosition)  =&gt; {
        if (to.hash) {
          return {selector: to.hash}
        } else {
          return {x: 0, y: 0}
        }
      },
      routes: [
        ....... 
        { path: &#39;/user/:id&#39;, component: UserView },
      ]
    })

  [1]: https://github.com/vuejs/vue-router


How to set URL query params in Vue with Vue-Router

How may I get information from a `ReadableStream` object? 

I am using the Fetch API and I don&#39;t see this to be clear from the documentation. 

The body is being returned as a `ReadableStream` and I would simply like to access a property within this stream. Under Response in the browser dev tools, I appear to have this information organised into properties, in the form of a JavaScript object. 

    fetch(&#39;http://192.168.5.6:2000/api/car&#39;, obj)
        .then((res) =&gt; {
            if(res.status == 200) {
                console.log(&quot;Success :&quot; + res.statusText);   //works just fine
            }
            else if(res.status == 400) {
                console.log(JSON.stringify(res.body.json());  //res.body is undefined.
            }

            return res.json();
        })

Retrieve data from a ReadableStream object?

Can someone explain when you would use a dispatch versus a commit?

I understand a commit triggers mutation, and a dispatch triggers an action.

However, isn&#39;t a dispatch also a type of action? 



Vuex 2.0 Dispatch versus Commit

What is the best way to get client&#39;s timezone and convert it to some other timezone when using moment.js and moment-timezone.js

I want to find out what is clients timezone and later convert his date and time into some other timezone.

Does anybody has experience with this?

Get timezone from users browser using moment(timezone).js

So I want to pass props to an Vue component, but I expect these props to change in future from inside that component e.g. when I update that Vue component from inside using AJAX. So they are only for initialization of component.


My `cars-list` Vue component element where I pass props with initial properties to `single-car`:

   
    // cars-list.vue

    &lt;script&gt;
        export default {
            data: function() {
                return {
                    cars: [
                        {
                            color: &#39;red&#39;,
                            maxSpeed: 200,
                        },
                        {
                            color: &#39;blue&#39;,
                            maxSpeed: 195,
                        },
                    ]
                }
            },
        }
    &lt;/script&gt;

    &lt;template&gt;
        &lt;div&gt;
            &lt;template v-for=&quot;car in cars&quot;&gt;
                &lt;single-car :initial-properties=&quot;car&quot;&gt;&lt;/single-car&gt;
            &lt;/template&gt;
        &lt;/div&gt;
    &lt;/template&gt;


The way I do it right now it that inside my `single-car` component I&#39;m assigning  `this.initialProperties` to my `this.data.properties` on `created()` initialization hook. And it works and is reactive.


    // single-car.vue

    &lt;script&gt;
        export default {
            data: function() {
                return {
                    properties: {},
                }
            },
            created: function(){
                this.data.properties = this.initialProperties;
            },
        }
    &lt;/script&gt;

    &lt;template&gt;
        &lt;div&gt;Car is in {{properties.color}} and has a max speed of {{properties.maxSpeed}}&lt;/div&gt;
    &lt;/template&gt;



But my problem with that is that I don&#39;t know if that&#39;s a correct way to do it? Won&#39;t it cause me some troubles along the road? Or is there a better way to do it?


What&#39;s the correct way to pass props as initial data in Vue.js 2?

I&#39;m using the [vue-cli scaffold for webpack](https://github.com/vuejs-templates/webpack)

My Vue component structure/heirarchy currently looks like the following:

- App
    - PDF Template
        - Background
        - Dynamic Template Image
        - Static Template Image
        - Markdown

At the app level, I want a vuejs component method that can aggregate all of the child component&#39;s data into a single JSON object that can be sent off to the server. 

**Is there a way to access child component&#39;s data? Specifically, multiple layers deep?**

If not, what is the best practice for passing down oberservable data/parameters, so that when it&#39;s modified by child components I have access to the new values? I&#39;m trying to avoid hard dependencies between components, so as of right now, the only thing passed using component attributes are initialization values.

**UPDATE:**

Solid answers. Resources I found helpful after reviewing both answers:

 - [Vuex and when to use it](https://vuex.vuejs.org/)
 - [Vuex alternative solution for smaller apps](https://vuejs.org/v2/guide/state-management.html#Simple-State-Management-from-Scratch)

VueJS access child component&#39;s data from parent

I have a [vuex][1] store, like following:

    import spreeApi from &#39;../../gateways/spree-api&#39;
    // initial state
    const state = {
      products: [],
      categories: []
    }
    
    // mutations
    const mutations = {
     SET_PRODUCTS: (state, response) =&gt; {
       state.products = response.data.products
       commit(&#39;SET_CATEGORIES&#39;)
     },
     SET_CATEGORIES: (state) =&gt; {
       state.categories = state.products.map(function(product) { return product.category})
     }
    
    }
    
    const actions = {
     FETCH_PRODUCTS: (state, filters) =&gt; {
       return spreeApi.get(&#39;products&#39;).then(response =&gt; state.commit(&#39;SET_PRODUCTS&#39;, response))
     }
    }
    
    export default {
      state,
      mutations,
      actions
    }

I want to call mutation: `SET_CATEGORIES` from mutation: `SET_PRODUCTS`, But this gives me error: 

&gt;projectFilter.js:22 Uncaught (in promise) ReferenceError: commit is not defined(…)

What should be correct way to do this. I tried `store.commit` and `this.commit`, but these also gave similar errors.

  [1]: https://vuex.vuejs.org/en/intro.html


Can I call commit from one of mutations in Vuex store

I have a javascript variable which I want to pass globally to Vue components upon instantiation thus either each registered component has it as a property or it can be accessed globally.

Note:: I need to set this global variable for vuejs as a **READ ONLY** property

Apply global variable to Vuejs

I&#39;m starting to play with vuejs (2.0).
I built a simple page with one component in it.
The page has one Vue instance with data.
On that page I registered and added the component to html. 
The component has one `input[type=text]`. I want that value to reflect on the parent (main Vue instance).

How do I correctly update the component&#39;s parent data?
Passing a bound prop from the parent is not good and throws some warnings to the console. They have something in their doc but it is not working.


vuejs update parent data from child component

I have a component with the following hash 

    { 
      computed: { 
        isUserID: { 
          get: function(){
             return this.userId? 
          } 
      }
    }

 

Should I be watching `isUserID` or `userId` for changes? Can you watch computed properties?

Watching computed properties

I want to bind a custom attribute to an option select menu.
The `&lt;option&gt;` tag would simply have an attribute of `selected=&quot;selected&quot;`

    &lt;template&gt;
      &lt;div&gt;
        &lt;select&gt;
          &lt;option v-for=&quot;&quot; v-bind:selected=&quot;[condition ? selected : notSelected]&quot; value=&quot;&quot;&gt;{{ resource.xprm_name }}&lt;/option&gt;
        &lt;/select&gt;
      &lt;/div&gt;
    &lt;/template&gt;

    data: {
      selected: &quot;selected&quot;,
      notSelected: &quot;&quot;
    }

This does not work, but if I change `v-bind:selected` to `v-bind:class` then it receives the appropriate class, so the logic is working, but not with the `selected` attribute. 

Any way to make it work with such custom attributes?

Content Type	Original Author	Original Content on Stackoverflow
Question	PeraMika	View Question on Stackoverflow
Solution 1 - Javascript	craig_h	View Answer on Stackoverflow
Solution 2 - Javascript	aurumpotestasest	View Answer on Stackoverflow
Solution 3 - Javascript	LastM4N	View Answer on Stackoverflow
Solution 4 - Javascript	tho-masn	View Answer on Stackoverflow

Default values for Vue component props & how to check if a user did not set the prop?

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Specify return type in TypeScript arrow function

BottomNavigationView display both icons and text labels at all times

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