I'm trying to concat two buffers with a space in between them in Node.js.
Here is my code.
var buff1 = new Buffer("Jumping");
var buff2 = new Buffer("Japang");
var buffSpace = new Buffer(1);
buffSpace[0] = "32";
var newBuff = Buffer.concat([buff1, buffSpace, buff2], (buff1.length + buff2.length + buffSpace.length));
console.log(newBuff.toString());
As per official doc, the first argument will be the Array list of Buffer objects. Hence I've created buffSpace for space.
Class Method: Buffer.concat(list[, totalLength])
list : Array List of Buffer objects to concat
totalLength: Number Total length of the buffers when concatenated
I'm getting the result as expected but not sure whether it is right way to do so. Please suggest if any better solution to achieve the same.
There are three changes I would suggest.
First, if you are using Node v6, use Buffer.from() instead of new Buffer(), as the latter is deprecated.
Second, you don't need to pass an argument for totalLength to Buffer.concat(), since it will be calculated automatically from the length of all of the buffers passed. While the docs note it will be faster to pass a total length, this will really only be true if you pass a constant value. What you are doing above is computing the length and then passing that, which is what the concat() function will do internally anyway.
Finally, I would recommend putting this in a function that works like Array.prototype.join(), but for buffers.
function joinBuffers(buffers, delimiter = ' ') {
let d = Buffer.from(delimiter);
return buffers.reduce((prev, b) => Buffer.concat([prev, d, b]));
}
And you can use it like this:
let buf1 = Buffer.from('Foo');
let buf2 = Buffer.from('Bar');
let buf3 = Buffer.from('Baz');
let joined = joinBuffers([buf1, buf2, buf3]);
console.log(joined.toString()); // Foo Bar Baz
Or set a custom delimiter like this:
let joined2 = joinBuffers([buf1, buf2, buf3], ' and ');
console.log(joined2.toString()); // Foo and Bar and Baz
Read the Buffer stream and save it to file as:
const data = [];
req.on('data', stream => {
data.push(stream);
});
req.on('close', () => {
const parsedData = Buffer.concat(data).toString('utf8');
fs.writeFileSync('./test.text', parsedData);
});
Related
The name list is supposedly as below:
Rose : 35621548
Jack : 32658495
Lita : 63259547
Seth : 27956431
Cathy: 75821456
Given you have a variable as StudentCode that contains the list above (I think const will do! Like:
const StudentCode = {
[Jack]: [32658495],
[Rose]: [35621548],
[Lita]: [63259547],
[Seth]: [27956431],
[Cathy]:[75821456],
};
)
So here are the questions:
1st: Ho can I define them in URL below:
https://www.mylist.com/student=?StudentCode
So the link for example for Jack will be:
https://www.mylist.com/student=?32658495
The URL is imaginary. Don't click on it please.
2nd: By the way the overall list is above 800 people and I'm planning to save an external .js file to be called within the current code. So tell me about that too. Thanks a million
Given
const StudentCode = {
"Jack": "32658495",
"Rose": "35621548",
"Lita": "63259547",
"Seth": "27956431",
"Cathy": "75821456",
};
You can construct urls like:
const urls = Object.values(StudentCode).map((c) => `https://www.mylist.com?student=${c}`)
// urls: ['https://www.mylist.com?student=32658495', 'https://www.mylist.com?student=35621548', 'https://www.mylist.com?student=63259547', 'https://www.mylist.com?student=27956431', 'https://www.mylist.com?student=75821456']
To get the url for a specific student simply do:
const url = `https://www.mylist.com?student=${StudentCode["Jack"]}`
// url: 'https://www.mylist.com?student=32658495'
Not sure I understand your second question - 800 is a rather low number so will not be any performance issues with it if that is what you are asking?
The properties of the object (after the trailing comma is removed) can be looped through using a for-in loop, (see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...in)
This gives references to each key of the array and the value held in that key can be referenced using objectName[key], Thus you will loop through your object using something like:
for (key in StudentCode) {
keyString = key; // e.g = "Jack"
keyValue = StudentCode[key]; // e.g. = 32658495
// build the urls and links
}
to build the urls, string template literals will simplify the process (see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Template_literals) allowing you to substitute values in your string. e.g.:
url = `https://www.mylist.com/student=?${StudentCode[key]`}
Note the use of back ticks and ${} for the substitutions.
Lastly, to build active links, create an element and sets its innerHTML property to markup built using further string template literals:
let link = `<a href=${url}>${keyValue}</a>`
These steps are combined in the working snippet here:
const StudentCode = {
Jack: 32658495,
Rose: 35621548,
Lita: 63259547,
Seth: 27956431,
Cathy: 75821456,
};
const studentLinks = [];
for (key in StudentCode) {
let url = `https://www.mylist.com/student=?${StudentCode[key]}`;
console.log(url);
studentLinks.push(`<a href href="url">${key}</a>`)
}
let output= document.createElement('div');
output.innerHTML = studentLinks.join("<br>");
document.body.appendChild(output);
I'm trying to use player data from a football stats API, but I can't seem to get data for the current season (which can be found in the last object in the array). For some reason I'm only getting data for the third index (code below).
.then(data => {
//BIO
const bio = data['data'][0]
const nameValue = bio['fullname']
const imageValue = bio['image_path']
const teamValue = bio['team']['data']['name']
const countryValue = bio['nationality']
const birthdateValue = bio['birthdate']
const heightValue = bio['height']
const positionValue = bio['position']['data']['name']
//STATS
const stats = bio['stats']['data']['data'.length - 1]
const appearancesValue = stats['appearences']
Here is an image of the JSON data I am trying to access. In this instance I should be getting data from [4] but I'm getting it from [3].
I'm quite inexperienced so I feel like I must be making a silly mistake somewhere! Appreciate any help.
the 'data'.length in the bio['stats']['data']['data'.length - 1] part will evaluate to the length of the "data" string. so it is always 4.
You most likely wanted the length of the array so it should be
bio['stats']['data'][bio['stats']['data'].length - 1]
Or you could extract it beforehand in a variable, for clarity
const dataLength = bio['stats']['data'].length;
const stats = bio['stats']['data'][dataLength - 1];
Also since you are using literals for the object properties you do not need to use the [] notation.
const dataLength = bio.stats.data.length;
const stats = bio.stats.data[dataLength - 1];
and you can do that with the rest of the code as well, to avoid typing all the ['..']
Building up on Henry Walker's answer.
Using the new JavaScript Array.at() method allows you to enter both positive and negative indices.
This code:
const dataLength = bio.stats.data.length;
const stats = bio.stats.data[dataLength - 1];
Would simply translate to:
const stats = bio.stats.data.at(-1);
Giving you the last element in the array.
As data object signifies, it has 5 objects in it, you can this particular object at 3rd place as in an array 1st value is stored at index 0. Try using this code to fetch the last object
var lastObject = bio.stats.data[bio.stats.data.length-1].player_id
I am trying to get string data from return values of AWS KMS call (Node.js SDK):
const pair = await kms.generateDataKeyPairWithoutPlaintext(params);
It returns both pair.PrivateKeyCiphertextBlob and pair.PublicKey as Uint8Array blobs. I need to make a base64 string out first and plain text out of the second.
I. think I got the first one:
const buff = Buffer.from(pair.PrivateKeyCiphertextBlob);
const privateKey = buff.toString('base64');
(though I am not sure) and I am really struggling to extract plain text out of the second. Something like
const publicKey = Buffer.from(pair.PublicKey).toString();
doesn't produce desired result.
Am I doing the first one right? How do I do the second one?
Ok, I realized what I actually needed is PEM. So I put together this function:
function generatePem (publicKeyBlob) {
const publicKeyInput= {
key: publicKeyBlob,
format: 'der',
type: 'spki'
}
const publicKeyObject = Crypto.createPublicKey(publicKeyInput);
const publicKeyExportOptions = {
format: 'pem',
type: 'spki'
}
const pemPublic = publicKeyObject.export(publicKeyExportOptions);
return pemPublic;
}
based on this gist. And I just pass pair.PublicKey as a parameter.
How could I rewrite this code to object javascript. Since Array usage is prohibed, I can only use objects here. Insted of pushing values to array, I would like to push this values into objects.
var container = [];
document.addEventListener("submit", function(e){
e.preventDefault();
});
window.addEventListener("load",function(){
var submit = document.getElementsByClassName("btn-primary");
submit[0].addEventListener("click",add,false);
document.getElementById("pobrisi").addEventListener("click",deleteAll,false);
var dateElement = document.getElementById('datum');
dateElement.valueAsDate = new Date();
var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1;
var yyyy = today.getFullYear();
if(dd<10){
dd='0'+dd
}
if(mm<10){
mm='0'+mm
}
today = yyyy+'-'+mm+'-'+dd;
dateElement.setAttribute("min",today);
});
function add() {
var title = document.getElementById("title").value;
var type = document.getElementById("type").value;
var datum = document.getElementById("datum").value.split("-");
datum = datum[2]+". "+datum[1]+". "+datum[0];
var data = new Book(title,type,datum);
container.push(data.add());
display();
}
function display(data) {
var destination = document.getElementById("list");
var html = "";
for(var i =0;i <container.length; i++) {
html +="<li>"+container[i]+"</li>";
}
destination.innerHTML = html;
}
function deleteAll(){
container=[];
document.getElementById("list").innerHTML="";
}
Wondering if is possible to write this code whitout any array usage.
initial remarks
The problem here, in my estimation, is that you haven't learned the fundamentals of data abstraction yet. If you don't know how to implement an array, you probably shouldn't be depending on one quite yet. Objects and Arrays are so widespread because they're so commonly useful. However, if you don't know what a specific data type is affording you (ie, what convenience does it provide?), then it's probable you will be misusing the type
If you take the code here but techniques like this weren't covered in your class, it will be obvious that you received help from an outside source. Assuming the teacher has a curriculum organized in a sane fashion, you should be able to solve problems based on the material you've already covered.
Based on your code, it's evident you really have tried much, but why do you think that people here will come up with an answer that your teacher will accept? How are we supposed to know what you can use?
a fun exercise nonetheless
OK, so (we think) we need an Array, but let's pretend Arrays don't exist. If we could get this code working below, we might not exactly have an Array, but we'd have something that works like an array.
Most importantly, if we could get this code working below, we'd know what it takes to make a data type that can hold a dynamic number of values. Only then can we begin to truly appreciate what Array is doing for us.
// make a list
let l = list(1) // (1)
// push an item on the end
l = push(l, 2) // (1 2)
// push another item on the end
l = push(l, 3) // (1 2 3)
// display each item of the list
listeach(l, function (x) {
console.log(x)
})
// should output
// 1
// 2
// 3
runnable demo
All we have to do is make that bit of code (above) work without using any arrays. I'll restrict myself even further and only use functions, if/else, and equality test ===. I see these things in your code, so I'm assuming it's OK for me to use them too.
But am I supposed to believe your teacher would let you write code like this? It works, of course, but I don't think it brings you any closer to your answer
var empty = function () {}
function isEmpty (x) {
return x === empty
}
function pair (x,y) {
return function (p) {
return p(x,y)
}
}
function head (p) {
return p(function (x,y) {
return x
})
}
function tail (p) {
return p(function (x,y) {
return y
})
}
function push (l, x) {
if (isEmpty(l))
return list(x)
else
return pair(head(l), push(tail(l), x))
}
function list (x) {
return pair(x, empty)
}
function listeach (l, f) {
if (isEmpty(l))
return null
else
(f(head(l)), listeach(tail(l), f))
}
// make a list
let l = list(1) // (1)
// push an item on the end
l = push(l, 2) // (1 2)
// push another item on the end
l = push(l, 3) // (1 2 3)
// display each item of the list
listeach(l, function (x) {
console.log(x)
})
closing remarks
It appears as tho you can use an Object in lieu of an Array. The accepted answer (at this time) shows a very narrow understanding of how an object could be used to solve your problem. After this contrived demonstration, are you confident that you are using Objects properly and effectively?
Do you know how to implement an object? Could you fulfill this contract (below)? What I mean by that, is could you write the functions object, set, and get such that the following expressions evaluated to their expected result?
In case it's not obvious, you're not allowed to use Object to make it happen. The whole point of the exercise is to make a new data type that you don't already have access to
m = object() // m
set(m, key, x) // m
get(m, key) // x
set(m, key2, y) // m
get(m, key2) // y
set(m, key3, set(object(), key4, z)) // m
get(get(m, key3), key4) // z
I'll leave this as an exercise for you and I strongly encourage you to do it. I think you will learn a lot in the process and develop a deep understanding and appreciation for what higher-level data types like Array or Object give to you
Since this is a homework I feel like I shouldn't solve it for you, but rather help you in the right direction.
Like Slasher mentioned you can use objects
With JavaScript object one book would look something like
const book = {
title: 'my awesome title',
type: 'novel'
};
book is the object
title is a property with a value 'my awesome title'
type is a property with a value 'novel'
But objects can also have other objects as values. Something like
const BookShelf= {
Book1: {
Title: 'my awesome title',
Type: 'novel'
},
Book2: {
Title: 'my horrible title',
Type: 'sci-fi'
}
};
You can reference the books in the bookshelf in two ways
const book1 = BookShelf.Book1 // Returns the book1 object
const title1 = Book1.Title; // Get the title
const sametitle = BookShelf.Book1.Title // Returns title for book1, same as above.
You can also use brackets:
const book1 = BookShelf['Book1'];
const title1 = BookShelf['Book1']['Title];
You can even make new properties on a object like this:
const Book3 = {
Title: 'running out of ideas'
Type: 'memoir'
};
BookShelf['Book3'] = Book3;
Now the BookShelf has a Book3 property. So your BookShelf object looks like
const BookShelf= {
Book1: {
Title: 'my awesome title',
Type: 'novel'
},
Book2: {
Title: 'my horrible title',
Type: 'sci-fi'
},
Book3 = {
Title: 'running out of ideas'
Type: 'memoir'
};
};
That should get you started :)
JavaScript Objects is a good way to go
1- define a new object:
var myVar = {};
or
var myVar = new Object();
2- usage
// insert a new value, it doesn't matter if the value is a string or int or even another object
// set a new value
myVar.myFirstValue="this is my first value";
// get existing value and do what ever you want with it
var value = myVar.myFirstValue
I'm trying to write a parser that supports the following type of query clauses
from: A person
at: a specific company
location: The person's location
So a sample query would be like -
from:Alpha at:Procter And Gamble location:US
How do i write this generic parser in javascript. Also, I was considering including AND operators inside queries like
from:Alpha AND at:Procter And Gamble AND location:US
However, this would conflict with the criteria value in any of the fields (Procter And Gamble)
Use a character like ";" instead of AND and then call theses functions:
var query = 'from:Alpha;at:Procter And Gamble;location:US';
var result = query.split(';').map(v => v.split(':'));
console.log(result);
And then you'll have an array of pairs, which array[0] = prop name and array[1] = prop value
var query = 'from:Alpha;at:Procter And Gamble;location:US';
var result = query.split(';').map(v => v.split(':'));
console.log(result);
Asuming your query will always look like this from: at: location:
You can do this:
const regex = /from:\s*(.*?)\s*at:\s*(.*?)\s*location:\s*(.*)\s*/
const queryToObj = query => {
const [,from,at,location] = regex.exec(query)
return {from,at,location}
}
console.log(queryToObj("from:Alpha at Betaat: Procter And Gamble location: US"))
However, adding a terminator allow you to mix order and lowering some keywords:
const regex = /(\w+):\s*(.*?)\s*;/g
const queryToObj = query => {
const obj = {}
let temp
while(temp = regex.exec(query)){
let [,key,value] = temp
obj[key] = value
}
return obj
}
console.log(queryToObj("from:Alpha at Beta;at:Procter And Gamble;location:US;"))
console.log(queryToObj("at:Procter And Gamble;location:US;from:Alpha at Beta;"))
console.log(queryToObj("from:Alpha at Beta;"))