Difference between “process.stdout.write” and “console.log” in node.js?

Difference between “process.stdout.write” and “console.log” in node.js?

What is the difference between “process.stdout.write” and “console.log” in node.js?
EDIT: Using console.log for a variable showed a lot of unreadable characters while using process.stdout.write showed an object.
Why is that?

Solutions/Answers:

Solution 1:

console.log() calls process.stdout.write with formatted output. See format() in console.js for the implementation.

Currently (v0.10.ish):

Console.prototype.log = function() {
  this._stdout.write(util.format.apply(this, arguments) + '\n');
};

Solution 2:

Looking at the Node docs apparently console.log is just process.stdout.write with a line-break at the end:

console.log = function (d) {
  process.stdout.write(d + '\n');
};

Source: http://nodejs.org/docs/v0.3.1/api/process.html#process.stdout

Solution 3:

I know this is a very old question but I didn’t see anybody talking about the main difference between process.stdout.write and console.log and I just want to mention it.

As Mauvis Leford and TK-421 pointed out, the console.log adds a line-break character at the end of the line (\n) but that’s not all what it does.

The code has not changed since at least 0.10.X version and now we have a a 5.X version.

Here is the code:

Console.prototype.log = function() {
  this._stdout.write(util.format.apply(this, arguments) + '\n');
};

As you can see, there is a part that says .apply(this, arguments) and that makes a big difference on functionality. It is easier to explain that with examples:

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process.stdout.write has a very basic functionality, you can just write something in there, like this:

process.stdout.write("Hello World\n"); 

If you don’t put the break line at the end you will get a weird character after your string, something like this:

process.stdout.write("Hello World"); //Hello World% 

(I think that means something like “the end of the program”, so you will see it only if you process.stdout.write was used at the end of your file and you didn’t add the break line)

On the other hand, console.log can do more.

  1. You can use it in the same way

    console.log("Hello World"); //You don't need the break line here because it was already formated and also that weird character did disappear

  2. You can write more than one string

    console.log("Hello", "World");

  3. You can make associations

    console.log("Hello %s", "World") //Useful when "World" is inside a variable

An that’s it, that added functionality is given thanks to the util.format.apply part (I could talk a lot about what exactly this does but you get my point, you can read more here).

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I hope somebody find this information useful.

Solution 4:

One big difference that hasn’t been mentioned is that process.stdout only takes strings as arguments (can also be piped streams), while console.log takes any Javascript data type.

e.g:

// ok
console.log(null)
console.log(undefined)
console.log('hi')
console.log(1)
console.log([1])
console.log({one:1})
console.log(true)
console.log(Symbol('mysymbol'))

// any other data type passed as param will throw a TypeError
process.stdout.write('1')

// can also pipe a readable stream (assuming `file.txt` exists)
const fs = require('fs')
fs.createReadStream('file.txt').pipe(process.stdout)

Solution 5:

Another important difference in this context would with process.stdout.clearLine() and process.stdout.cursorTo(0).

This would be useful if you want to show percentage of download or processing in the only one line. If you use clearLine(), cursorTo() with console.log() it doesn’t work because it also append \n to the text. Just try out this example:

var waitInterval = 500;
var totalTime = 5000;
var currentInterval = 0;

function showPercentage(percentage){
    process.stdout.clearLine();
    process.stdout.cursorTo(0);
    console.log(`Processing ${percentage}%...` ); //replace this line with process.stdout.write(`Processing ${percentage}%...`);
}

var interval = setInterval(function(){
 currentInterval += waitInterval;
 showPercentage((currentInterval/totalTime) * 100);
}, waitInterval);

setTimeout(function(){
 clearInterval(interval); 
}, totalTime);

Solution 6:

I’ve just noticed something while researching this after getting help with https.request for post method. Thought I share some input to help understand.

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process.stdout.write doesn’t add a new line while console.log does, like others had mentioned. But there’s also this which is easier to explain with examples.

var req = https.request(options, (res) => {
    res.on('data', (d) => {
        process.stdout.write(d);
        console.log(d)
    });
});

process.stdout.write(d); will print the data properly without a new line. However console.log(d) will print a new line but the data won’t show correctly, giving this <Buffer 12 34 56... for example.

To make console.log(d) show the information correctly, I would have to do this.

var req = https.request(options, (res) => {
    var dataQueue = "";    
    res.on("data", function (d) {
        dataQueue += d;
    });
    res.on("end", function () {
        console.log(dataQueue);
    });
});

So basically:

  • process.stdout.write continuously prints the information as the data being retrieved and doesn’t add a new line.

  • console.log prints the information what was obtained at the point of retrieval and adds a new line.

That’s the best way I can explain it.