Write javascript code with high performance

Write javascript code with high performance

Write javascript code with high performance - Premature optimization is the root of all evil. It's also the root of this article...

I like programming puzzles. I also like to go fast. We're going to take some LeetCode problems and solve them a few times, first improving runtime complexity in broad strokes and then looking for minor optimizations. We're after these wonderful words:

faster than 100.00% of JavaScript online submissions

The environment we're targetting is nodejs 10.15.0 with --harmony(source). The online judge system uses relatively small inputs for test cases as far as I can tell.

First problem

771. Jewels and Stones ~ You're given strings <em>J</em> representing the types of stones that are jewels, and <em>S</em> representing the stones you have. Each character in <em>S</em> is a type of stone you have. You want to know how many of the stones you have are also jewels.

A naive solution here is to loop through our stones, looping through the jewels for every stone. We'll be using standard for loops in this article as they are generally the fastest way of iterating data in JavaScript.

var numJewelsInStones = function(J, S) {
    let myJewels = 0;
    // Jewels
    for (var i = 0; i < J.length; i++) {
        // Stones
        for (var j = 0; j < S.length; j++) { // Nested!
            if (J[i] === S[j]) {
                myJewels++;
            }
        }
    }
    return myJewels;
};

The runtime is quadratic, O(N^2). Their online judge won't actually accept this solution! We get a big fat Time Limit Exceeded. Lesson? Nested for-loops should be avoided where possible.

Let's grab a Set to get rid of one of the loops. Reducing our runtime down to linear, O(N). Looking up a Set in JavaScript is constant time, O(1).

var numJewelsInStones = function(J, S) {
    const jewels = new Set(J); // Set accepts an iterable object
    let myJewels = 0;
    for (var i = 0; i < S.length; i++) {
        if (jewels.has(S[i])) {
            myJewels++;
        }
    }
    return myJewels;
};

For this effort, we're rewarded with faster than 97.84%. I'm happy with this code. It's efficient and readable. If I needed drastically better performance, I might reach for a different technology than JavaScript. We have to walk the length of both strings at least once and there's no getting around that. We can't beat O(N) but we can make optimizations.

The stones and jewels are defined as letters. So a-z and A-Z. This means there are just 52 different buckets our values can fall into! We can use a boolean array instead of a Set. To convert an alphabetical letter into a number, we'll use its ASCII code point via charCodeAt. We'll set an index to true to represent a jewel.

However, there aren't boolean arrays in JavaScript. We could use a standard array and initialize it to length 52. Or we could use Int8Array and allow the compiler to make additional optimizations. The typed array was ~6% faster when benchmarked with a range 0-52 of random characters entered as Jand S.

Did you spot that our length is wrong? This is something I forgot as I was testing. There are seven characters between z and A on the ASCII code chart so the length required is actually 59.

var numJewelsInStones = function(J, S) {
    const jewels = new Int8Array(59);
    for (var i = 0; i < J.length; i++) {
        jewels[J.charCodeAt(i)-65] = 1;
    }
    let myJewels = 0;
    for (var i = 0; i < S.length; i++) {
        if (jewels[S.charCodeAt(i)-65] === 1) {
            myJewels++;
        }
    }
    return myJewels;
};

Et voila, our 100% fastest submission. In my tests, this was actually twice as faster as the Set version. Other optimizations I skipped testing were caching lengths, using a while loop instead of a for loop, and placing the incrementor before the number (++myJewels vs myJewels++).

Second problem

345. Reverse Vowels of a String ~ Write a function that takes a string as input and reverse only the vowels of a string.

A naive solution for this might be to loop through the array twice, replacing on the second loop. Let's try that out first.

var reverseVowels = function(s) {
    const vowels = new Set(['a','e','i','o','u', 'A', 'E', 'I', 'O', 'U']);
    const reversed = [];
    let vowelsFound = [];
    // Find any vowels
    for (var i = 0; i < s.length; i++) {
        if (vowels.has(s[i])) {
            vowelsFound.push(s[i]);
        }   
    }
    // Build the final string
    for (var i = 0; i < s.length; i++) {
        if (vowels.has(s[i])) {
            reversed.push(vowelsFound.pop());
        } else {
            reversed.push(s[i]);
        }
    }
    return reversed.join('');
};

This nets us faster than 97.00%. The runtime is linear, O(2N) -> O(N), and it reads well but I can't help but think we're looping the string one more time than we have to. Let's try a two-pointer approach. Walking in, step-by-step, from the front and back at the same time, swapping any vowels we see. If there's a middle vowel we just leave it.

var reverseVowels = function(s) {
    const vowels = new Set(['a','e','i','o','u', 'A', 'E', 'I', 'O', 'U']);
    s = s.split('');
    let front = 0;
    let back = s.length - 1;
    while (front < back) {
        if (!vowels.has(s[front])) {
            front++;
            continue;
        }
        if (!vowels.has(s[back])) {
            back--;
            continue;
        }
        let temp = s[front];
        s[front] = s[back];
        s[back] = temp;
        front++;
        back--;
    }
    return s.join('');
};

We've reduced a full iteration! This gets us faster than 98.89% and it's at this point that we need to remember that LeetCode's benchmarks aren't conclusive nor are they consistent. It's not feasible for them to run a large number of iterations with a mixture of test cases. If you're practicing your puzzle solving, stop at 97% and up. But that's not the point of this article, and, reader, I'm going to get that 100% for you.

First I threw out the Set. The number of vowels is constant and we don't need all that hashing going on. I tried a switch statement but then found a chained if statement was faster. I discovered that in-lining this logic was faster than a function. I then reduced this down to an expression. What I'm trying to say is: the code coming up is gross. It's close-down-your-IDE-and-talk-a-walk gross. But .. it's faster than 100.00%.

var reverseVowels = function(s) {
    s = s.split('');
    let front = 0;
    let back = s.length - 1;
    while (front < back) {
        if (s[front] !== 'a' &&
            s[front] !== 'e' &&
            s[front] !== 'i' &&
            s[front] !== 'o' &&
            s[front] !== 'u' &&
            s[front] !== 'A' &&
            s[front] !== 'E' &&
            s[front] !== 'I' &&
            s[front] !== 'O' &&
            s[front] !== 'U') {
            front++;
            continue;
        }
        if (s[back] !== 'a' &&
            s[back] !== 'e' &&
            s[back] !== 'i' &&
            s[back] !== 'o' &&
            s[back] !== 'u' &&
            s[back] !== 'A' &&
            s[back] !== 'E' &&
            s[back] !== 'I' &&
            s[back] !== 'O' &&
            s[back] !== 'U') {
            back--;
            continue;
        }
        let temp = s[front];
        s[front++] = s[back];
        s[back--] = temp;
    }
    return s.join('');
};

(I'm sorry).

Third problem

509. Fibonacci Number ~ Calculate the nth Fibonacci number.

This is a common puzzle and it was the hardest to improve the runtime for because there are so few moving parts in the final solution. I'm sure some RNG was involved with LeetCode's grading too. Let's get the naive solution out of the way. The Fibonacci sequence is often used to teach recursion. However, the algorithm that is used has a runtime of O(2^n) (very slow).

I actually crashed a browser tab by trying to calculate the 50th term with this function.

var fib = function(N) {
    if (N < 2) {
        return N;
    }
    return fib(N - 1) + fib(N - 2);
}

We get faster than 36.63% for this answer. Ouch. In production, this is the kind of puzzle that can be solved by memoization (caching some of the work for later). This is the best solution because we only calculate up to the values that we need in linear time O(N) and then running the algorithm again for a term under that limit is constant time O(1).

const memo = [0, 1];
var fib = function(N) {
    if (memo[N] !== undefined) {
        return memo[N];
    }
    const result = fib(N - 1) + fib(N - 2);
    memo[N] = result;
    return result
};

faster than 94.25%. LeetCode doesn't store data between each run-through of our code so we'll have to try something different. We've interested in calculating one number of the sequence just once. I think we can throw away that array. Let's look at the iterative solution.

var fib = function(N) {
    if (N < 2) {
        return N;
    }
    let a = 1;
    let b = 1;
    for (let i = 3; i <= N; ++i) {
        a = a + b;
        b = a - b;
    }
    return a;
};

If this looks a little different to other iterative versions you might have seen, it's because I avoided the third temporary variable that we have to use in JavaScript to swap values (there are other methods as well but they're too slow). I did some benchmarks and I found using arithmetic instead was..faster than 100.00%.

JavaScript Tutorial: if-else Statement in JavaScript

JavaScript Tutorial: if-else Statement in JavaScript

This JavaScript tutorial is a step by step guide on JavaScript If Else Statements. Learn how to use If Else in javascript and also JavaScript If Else Statements. if-else Statement in JavaScript. JavaScript's conditional statements: if; if-else; nested-if; if-else-if. These statements allow you to control the flow of your program's execution based upon conditions known only during run time.

Decision Making in programming is similar to decision making in real life. In programming also we face some situations where we want a certain block of code to be executed when some condition is fulfilled.
A programming language uses control statements to control the flow of execution of the program based on certain conditions. These are used to cause the flow of execution to advance and branch based on changes to the state of a program.

JavaScript’s conditional statements:

  • if
  • if-else
  • nested-if
  • if-else-if

These statements allow you to control the flow of your program’s execution based upon conditions known only during run time.

  • if: if statement is the most simple decision making statement. It is used to decide whether a certain statement or block of statements will be executed or not i.e if a certain condition is true then a block of statement is executed otherwise not.
    Syntax:
if(condition) 
{
   // Statements to execute if
   // condition is true
}

Here, condition after evaluation will be either true or false. if statement accepts boolean values – if the value is true then it will execute the block of statements under it.
If we do not provide the curly braces ‘{‘ and ‘}’ after if( condition ) then by default if statement will consider the immediate one statement to be inside its block. For example,

if(condition)
   statement1;
   statement2;

// Here if the condition is true, if block 
// will consider only statement1 to be inside 
// its block.

Flow chart:

Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate If statement 

var i = 10; 

if (i > 15) 
document.write("10 is less than 15"); 

// This statement will be executed 
// as if considers one statement by default 
document.write("I am Not in if"); 

< /script> 

Output:

I am Not in if
  • if-else: The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But what if we want to do something else if the condition is false. Here comes the else statement. We can use the else statement with if statement to execute a block of code when the condition is false.
    Syntax:
if (condition)
{
    // Executes this block if
    // condition is true
}
else
{
    // Executes this block if
    // condition is false
}


Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate If-else statement 

var i = 10; 

if (i < 15) 
document.write("10 is less than 15"); 
else
document.write("I am Not in if"); 

< /script> 

Output:

i is smaller than 15
  • nested-if A nested if is an if statement that is the target of another if or else. Nested if statements means an if statement inside an if statement. Yes, JavaScript allows us to nest if statements within if statements. i.e, we can place an if statement inside another if statement.
    Syntax:
if (condition1) 
{
   // Executes when condition1 is true
   if (condition2) 
   {
      // Executes when condition2 is true
   }
}

Example:

<script type = "text/javaScript"> 

// JavaScript program to illustrate nested-if statement 

var i = 10; 

if (i == 10) { 

// First if statement 
if (i < 15) 
	document.write("i is smaller than 15"); 

// Nested - if statement 
// Will only be executed if statement above 
// it is true 
if (i < 12) 
	document.write("i is smaller than 12 too"); 
else
	document.write("i is greater than 15"); 
} 
< /script> 

Output:

i is smaller than 15
i is smaller than 12 too
  • if-else-if ladder Here, a user can decide among multiple options.The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
if (condition)
    statement;
else if (condition)
    statement;
.
.
else
    statement;


Example:

<script type = "text/javaScript"> 
// JavaScript program to illustrate nested-if statement 

var i = 20; 

if (i == 10) 
document.wrte("i is 10"); 
else if (i == 15) 
document.wrte("i is 15"); 
else if (i == 20) 
document.wrte("i is 20"); 
else
document.wrte("i is not present"); 
< /script> 

Output:

i is 20

How to Retrieve full Profile of LinkedIn User using Javascript

How to Retrieve full Profile of LinkedIn User using Javascript

I am trying to retrieve the full profile (especially job history and educational qualifications) of a linkedin user via the Javascript (Fetch LinkedIn Data Using JavaScript)

Here we are fetching LinkedIn data like Username, Email and other fields using JavaScript SDK.

Here we have 2 workarounds.

  1. Configuration of linkedIn developer api
  2. Javascript Code to fetch records

Configuration of linkedIn developer api

In order to fetch records, first we need to create developer api in linkedin which will act as token/identity while fetching data from other linkedin accounts.

So to create api, navigate to https://linkedin.com/developer/apps and click on 'Create Application'.

After navigating, fill in details like name, description and other required fields and then submit.

As we submit, it will create Client ID and Client Secret shown below, which we will be using in our code while communicating to fetch records from other LinkedIn account.

Note: We need to provide localhost Url here under Oauth 2.0. I am using my localhost, but you can probably use other production URLs under Oauth 2.0 where your app is configured. It will make your api  consider the Url as trusted which fetching records.

Javascript Code to fetch records

For getting user details like first name, last name,User image can be written as,

<script type="text/javascript" src="https://platform.linkedin.com/in.js">  
    api_key: XXXXXXX //Client ID  
    onLoad: OnLinkedInFrameworkLoad //Method that will be called on page load  
    authorize: true  
</script>  
<script type="text/javascript">  
    function OnLinkedInFrameworkLoad() {  
        IN.Event.on(IN, "auth", OnLinkedInAuth);  
    }  
  
    function OnLinkedInAuth() {  
        IN.API.Profile("me").result(ShowProfileData);  
    }  
  
    function ShowProfileData(profiles) {  
        var member = profiles.values[0];  
        var id = member.id;  
        var firstName = member.firstName;  
        var lastName = member.lastName;  
        var photo = member.pictureUrl;  
        var headline = member.headline;  
        //use information captured above  
        var stringToBind = "<p>First Name: " + firstName + " <p/><p> Last Name: " + lastName + "<p/><p>User ID: " + id + " and Head Line Provided: " + headline + "<p/>"  
        document.getElementById('profiles').innerHTML = stringToBind;  
    }  
</script>    

Kindly note we need to include 'https://platform.linkedin.com/in.js' as src under script type as it will act on this Javascript SDK provided by Linkedin.

In the same way we can also fetch records of any organization with the companyid as keyword.

<head>  
    <script type="text/javascript" src="https://platform.linkedin.com/in.js">  
        api_key: XXXXXXX ////Client ID  
        onLoad: onLinkedInLoad  
        authorize: true  
    </script>  
</head>  
  
<body>  
    <div id="displayUpdates"></div>  
    <script type="text/javascript">  
        function onLinkedInLoad() {  
            IN.Event.on(IN, "auth", onLinkedInAuth);  
            console.log("On auth");  
        }  
  
        function onLinkedInAuth() {  
            var cpnyID = XXXXX; //the Company ID for which we want updates  
            IN.API.Raw("/companies/" + cpnyID + "/updates?event-type=status-update&start=0&count=10&format=json").result(displayCompanyUpdates);  
            console.log("After auth");  
        }  
  
        function displayCompanyUpdates(result) {  
            var div = document.getElementById("displayUpdates");  
            var el = "<ul>";  
            var resValues = result.values;  
            for (var i in resValues) {  
                var share = resValues[i].updateContent.companyStatusUpdate.share;  
                var isContent = share.content;  
                var isTitled = isContent,  
                    isLinked = isContent,  
                    isDescription = isContent,  
                    isThumbnail = isContent,  
                    isComment = isContent;  
                if (isTitled) {  
                    var title = isContent.title;  
                } else {  
                    var title = "News headline";  
                }  
                var comment = share.comment;  
                if (isLinked) {  
                    var link = isContent.shortenedUrl;  
                } else {  
                    var link = "#";  
                }  
                if (isDescription) {  
                    var description = isContent.description;  
                } else {  
                    var description = "No description";  
                }  
                /* 
                if (isThumbnailz) { 
                var thumbnailUrl = isContent.thumbnailUrl; 
                } else { 
                var thumbnailUrl = "http://placehold.it/60x60"; 
                } 
                */  
                if (share) {  
                    var content = "<a target='_blank' href=" + link + ">" + comment + "</a><br>";  
                    //el += "<li><img src='" + thumbnailUrl + "' alt=''>" + content + "</li>";  
                    el += "<li><div>" + content + "</div></li>";  
                }  
                console.log(share);  
            }  
            el += "</ul>";  
            document.getElementById("displayUpdates").innerHTML = el;  
        }  
    </script>  
</body>  

We can get multiple metadata while fetching records for any any organization. We can get company updates as shown below.

Conclusion

We can also fetch any company specific data like company job updates/post, total likes, comments, and number of views along with a lot of metadata we can fetch which I have shown below.

Thank you for reading !

7 Best Javascript Iframe Libraries

7 Best Javascript Iframe Libraries

Iframes let you build user experiences into embeddable ‘cross-domain components’, which let users interact with other sites without being redirected. I have compiled 7 best Javascript iframe libraries.

Iframes let you build user experiences into embeddable ‘cross-domain components’, which let users interact with other sites without being redirected. I have compiled 7 best Javascript iframe libraries.

1. Zoid

A cross-domain component toolkit, supporting:

  • Render an iframe or popup on a different domain, and pass down props, including objects and functions
  • Call callbacks natively from the child window without worrying about post-messaging or cross-domain restrictions
  • Create and expose components to share functionality from your site to others!
  • Render your component directly as a React, Vue or Angular component!
    It's 'data-down, actions up' style components, but 100% cross-domain using iframes and popups!

Download


2. Postmate

Postmate is a promise-based API built on postMessage. It allows a parent page to speak with a child iFrame across origins with minimal effort.

Download


3. Iframe Resizer

Keep same and cross domain iFrames sized to their content with support for window/content resizing, in page links, nesting and multiple iFrames

Demo

Download


4. Iframely

Embed proxy. Supports over 1800 domains via custom parsers, oEmbed, Twitter Cards and Open Graph

Demo

Download


5. React Frame component

This component allows you to encapsulate your entire React application or per component in an iFrame.

Demo

Download


6. Seamless.js

A seamless iframe makes it so that visitors are unable to distinguish between content within the iframe and content beside the iframe. Seamless.js is a JavaScript library (with no dependencies) that makes working with iframes easy by doing all the seamless stuff for you automatically.

Demo

Download


7. Porthole

A proxy to safely communicate to cross-domain iframes in javascript

Demo

Download


Thank for read!