`fs.writeFileSync` and `fs.writeFile` overwrite the file by default, there is no need for extra checks if this is what you want to do. This is mentioned in the docs:

[fs.writeFile](https://nodejs.org/api/fs.html#fs_fs_writefile_file_data_options_callback)

&gt; Asynchronously writes data to a file, replacing the file if it already exists.



Found the solution.
fs.writeFileSync gets a third arguments for options that can be an object.
So if you get the &quot;File already exist&quot; you should do.

    fs.writeFileSync(path,content,{encoding:&#39;utf8&#39;,flag:&#39;w&#39;})
    

When you say &quot;best way&quot;, i think at performance and scalability and i&#39;d say use the &lt;a href=&quot;https://stackoverflow.com/questions/35178903/overwrite-a-file-in-node-js&quot;&gt;asynchronous method&lt;/a&gt;

 

`fs.writeFileSync(path,string)` as the name suggest is synchronous (blocking api) the thread is held for the whole lifecycle of the request, that means your nodejs thread will be blocked until the operation finishes and this behavior in a production environment with simultaneous connections from multiple clients could kill your app.

Do not think at the single line of code, less code doesn&#39;t mean better performance.

I have the following Sass snippet in which I want the `&lt;thead&gt;` to float as the table scrolls. This works properly in Safari, but not in Chrome `Version 58.0.3029.110 (64-bit)`.

I know that Chrome has had on-again-off-again support for `sticky`, and currently supports it, but is it final? Is this a Chrome bug or do I need a different solution? (I prefer the CSS approach rather than Javascript because it&#39;s more performant.)

    .table {
      thead {
        background: white;
        position: sticky;
        top: 0;
        z-index: 10;
      }
    }

CSS-Only Sticky Table Headers In Chrome

The JavaScript Date object compare dates with time including, so, if you compare:
`time1.getTime() === time2.getTime()`, they&#39;ll be **&quot;false&quot;** if at least one millisecond is different.

What we need is to have a nice way to compare by Hour, Day, Week, Month, Year?
Some of them are easy, like year: `time1.getYear() === time2.getYear()`
but with day, month, hour it is more complex, as it requires multiple validations or divisions.

Is there any nice module or optimized code for doing those comparisons?

How to tell if two dates are in the same day or in the same hour?

I&#39;m trying to overwrite an existing file.
I&#39;m first checking if the file exists using:

    fs.existsSync(path)

If file does not exit I&#39;m creating and writing using:

    fs.writeFileSync(path,string) 

The problem is when the file already exists and I want to over write all its contents.
Is there a single line solution, so far I searched and found solutions that use 
fs.truncate &amp; fs.write, but is there a one hit solution?

What&#39;s the best way to overwrite a file using fs in node.js

I'm trying to overwrite an existing file.
I'm first checking if the file exists using:
<pre><code class="hljs language-lua">fs.existsSync(path)
</code></pre>
If file does not exit I'm creating and writing using:
<pre><code class="hljs language-lua">fs.writeFileSync(path,string) 
</code></pre>
The problem is when the file already exists and I want to over write all its contents.
Is there a single line solution, so far I searched and found solutions that use
fs.truncate &#x26; fs.write, but is there a one hit solution?

I&#39;ve a function like this:

    function top() {
      
      //promise1
      ParentPromise({
        ...some code here...
      }).then(function() {
    
    
        //promise2
            ChildPromise({
              ..some code here...
            }).then(function(response) {
             var result = response.result.items;
             
            });
          
    });
    
    };

and i need to return result value in this way:

    var myresult = start();
How i can do that? THX

Promise inside promise: what&#39;s the correct way to return a variable from the child promise? (JS)

I have the following express endpoint for uploading to Google Cloud storage. It works great and the response from the google api gives me a unique file name that I want to pass back to my front end:

    app.post(&#39;/upload&#39;, (req, res) =&gt; {
      var form = new formidable.IncomingForm(),
      files = [],
      fields = [];

      form
        .on(&#39;field&#39;, function(field, value) {
          fields.push([field, value]);
        })
        .on(&#39;file&#39;, function(field, file) {
          files.push([field, file]);
        })
        .on(&#39;end&#39;, function() {
          console.log(&#39;-&gt; upload done&#39;);
        });
      form.parse(req, function(err, fields, files){
        var filePath = files.file.path;
        bucket.upload(filePath, function(err, file, apiResponse){
          if (!err){
            res.writeHead(200, {&#39;content-type&#39;: &#39;text/plain&#39;});
            res.end(&quot;Unique File Name:&quot; + file.name);
          }else{
            res.writeHead(500);
            res.end();
          }
        });
      });
  
     return;
    });

I reach this endpoint by calling a short function which passes the file to it: 

    function upload(file) {
      var data = new FormData();
      data.append(&#39;file&#39;, file);
      return fetch(`upload`,{
        method: &#39;POST&#39;,
        body: data
      });
    }

    const Client = { upload };
    export default Client;

This function is called from my front end like this: 
					
    Client.upload(this.file).then((data) =&gt; {
	  console.log(data);
	});

This final `console.log(data)` logs the response to the console. However, I don&#39;t see anywhere the response that I wrote in (`&quot;Unique File Name:&quot; + file.name`)

How I can retrieve this info from the response body on the client-side? 



The `data` looks like this when I console.log it:

[![Screenshot of the data console.log][1]][1]


This is the response I get when I POST a file to my endpoint using Postman:

[![Screen shot of response using Postman][2]][2]


  [1]: https://i.stack.imgur.com/0wl4a.png
  [2]: https://i.stack.imgur.com/pEsyV.png

Read the body of a Fetch Promise

For an example, to set a style in react you could do

`var css = {color: red}`
   
and 

`&lt;h1 style={css}&gt;Hello world&lt;/h1&gt;`

Why do you need the curly braces around css in the second code snippet?

What do curly braces mean in JSX (React)?

I&#39;ve a lot of tables in [Lovefield][1] and their respective Interfaces for what columns they have.

Example:

&lt;!-- language: lang-ts --&gt;

    export interface IMyTable {
      id: number;
      title: string;
      createdAt: Date;
      isDeleted: boolean;
    }

I&#39;d like to have the property names of this interface in an array like this:

&lt;!-- language: lang-ts --&gt;

    const IMyTable = [&quot;id&quot;, &quot;title&quot;, &quot;createdAt&quot;, &quot;isDeleted&quot;];


I cannot make an object/array based on the interface `IMyTable` directly which should do the trick because I&#39;d be getting the interface names of the tables dynamically. Hence I need to iterate over these properties in the interface and get an array out of it.

How do I achieve this result?


  [1]: https://github.com/google/lovefield


Get keys of a Typescript interface as array of strings

I&#39;m creating a component with [Vue.js][1]. 

When I reference `this` in any of the the [lifecycle hooks][2] (`created`, `mounted`, `updated`, etc.) it evaluates to `undefined`:

    mounted: () =&gt; {
      console.log(this); // logs &quot;undefined&quot;
    },

---

The same thing is also happening inside my computed properties:

    computed: {
      foo: () =&gt; { 
        return this.bar + 1; 
      } 
    }

I get the following error:

&gt; Uncaught TypeError: Cannot read property &#39;bar&#39; of undefined

Why is `this` evaluating to `undefined` in these cases?


  [1]: https://vuejs.org/v2/guide/
  [2]: https://vuejs.org/v2/api/#Options-Lifecycle-Hooks

VueJS: why is &quot;this&quot; undefined?

`yarn install -h` suggests that the `-g` (global) option is `DEPRECATED`. How am I supposed to indicate that I want a bunch of packages (from `package.json` / `yarn.lock` files) to be installed globally?

Options I saw:

- `yarn global [command]` has things such as `ls` and `add` but not `install`. `add` only works with particular package names, if I understand correctly. I already have my `yarn.lock` file ready, I don&#39;t want to repeat myself on the command line.
- `yarn global add` each package one by one. Now my list of packages would be imperative instead of declarative.

Specifically, I&#39;d like to use one executable from one of those packages.

How to install a list of many global packages with Yarn

I had created firebase functions in nodejs and deployed the code on firebase.
The function was to send an email when the new user is created.
I have lost the code now. Can we pull that code from firebase ?

Get code from firebase console which I deployed earlier

I am doing a quick stress test on two (kinda) hello world projects written in [tag:node.js] and [tag:asp.net-core]. Both of them are running in production mode and without a logger attached to them. The result is astonishing! ASP.NET core is outperforming node.js app even after doing some extra work whereas the node.js app is just rendering a view.

# App 1: `http://localhost:3000/nodejs` `node.js`
**Using**: node.js, express and vash rendering engine.

[![nodejs app][1]][1]


The code in this endpoint is

    router.get(&#39;/&#39;, function(req, res, next) {
      var vm = {
        title: &#39;Express&#39;,
        time: new Date()
      }
      res.render(&#39;index&#39;, vm);
    });

As you can see, it does nothing apart from sending current date via the `time` variable to the view.

# App 2: `http://localhost:5000/aspnet-core` `asp.net core`
**Using**: ASP.NET Core, default template targeting `dnxcore50`

However this app does something other than just rendering a page with a date on it. It generates 5 paragraphs of various random texts. This should theoretically make this little bit heavier than the nodejs app.

[![asp.net core app][2]][2]

Here is the action method that render this page

    [ResponseCache(Location = ResponseCacheLocation.None, NoStore = true)]
    [Route(&quot;aspnet-core&quot;)]
    public IActionResult Index()
    {
        var sb = new StringBuilder(1024);
        GenerateParagraphs(5, sb);
    
        ViewData[&quot;Message&quot;] = sb.ToString();
        return View();
    }

# Stress test result

## Node.js App stress test result

Update: [Following suggestion by Gorgi Kosev][3]

Using `npm install -g recluster-cli &amp;&amp; NODE_ENV=production recluster-cli app.js 8`

[![nodejs test 2][4]][4]

## ASP.NET Core App stress test result

[![asp.net core stress test result][5]][5]

Can&#39;t believe my eyes! It can&#39;t be true that in this basic test asp.net core is way faster than nodejs. Off course this is not the only metric used to measure performance between these two web technologies, but I am wondering **what am I doing wrong in the node.js side?**.

Being a professional asp.net developer and wishing to adapt node.js in personal projects, this is kind of putting me off - as I&#39;m a little paranoid about performance. I thought node.js is faster than asp.net core (in general - as seen in various other benchmarks) I just want to prove it to myself (to encourage myself in adapting node.js). 

Please reply in comment if you want me to include more code snippets.

**Update:**
**Time distribution of .NET Core app**

[![aspnetcore app time distribution][6]][6]

**Server response**

    HTTP/1.1 200 OK
    Cache-Control: no-store,no-cache
    Date: Fri, 12 May 2017 07:46:56 GMT
    Pragma: no-cache
    Transfer-Encoding: chunked
    Content-Type: text/html; charset=utf-8
    Server: Kestrel


  [1]: https://i.stack.imgur.com/Wuxhh.png
  [2]: https://i.stack.imgur.com/I5TnV.png
  [3]: https://stackoverflow.com/questions/43920942/unexpected-outcome-of-node-js-vs-asp-net-core-performance-test?noredirect=1#comment75157955_43920942
  [4]: https://i.stack.imgur.com/zTLuH.png
  [5]: https://i.stack.imgur.com/fajFZ.png
  [6]: https://i.stack.imgur.com/tlSDf.png

Unexpected outcome of node.js vs ASP.NET Core performance test

I am asking this question because I and my colleague have a dispute on coding style because he prefers arrows function declaration:

    const sum = (a, b) =&gt; a + b;

And I prefer old-style standalone function declaration:

    function sum(a, b) {
        return a + b;
    }

My point is that code in old-style more readable and you can more clearly distinguish function and variable declarations. His point is that code with arrow functions just run faster.

Do you know something about actual performance penalties (in v8) when you use old-style standalone function declaration instead of arrow functions? Are that penalties really exists?

Content Type	Original Author	Original Content on Stackoverflow
Question	Tomas Katz	View Question on Stackoverflow
Solution 1 - Javascript	mihai	View Answer on Stackoverflow
Solution 2 - Javascript	Tomas Katz	View Answer on Stackoverflow
Solution 3 - Javascript	Karim	View Answer on Stackoverflow

What's the best way to overwrite a file using fs in node.js

Javascript Problem Overview

Javascript Solutions

Solution 1 - Javascript

Solution 2 - Javascript

Solution 3 - Javascript

How to tell if two dates are in the same day or in the same hour?

CSS-Only Sticky Table Headers In Chrome

Attributions