How to use JavaScript Proxies

How to use JavaScript Proxies

What is a JavaScript proxy? The Proxy object is used to define custom behavior for fundamental operations (e.g. property lookup, assignment, enumeration, function invocation, etc).

What is a JavaScript proxy? The Proxy object is used to define custom behavior for fundamental operations (e.g. property lookup, assignment, enumeration, function invocation, etc).

There’s a very recent new feature of the JavaScript language that is still not being widely used: JavaScript proxies.

With JavaScript proxies you can wrap an existing object and intercept any access to its attributes or methods. Even if they do not exist! 💥

You can intercept calls to methods that do not exist

👋 Hello World JavaScript Proxy

Let’s start with the basics. A ‘hello world’ example could be:

const wrap = obj => {
  return new Proxy(obj, {
    get(target, propKey) {
        console.log(`Reading property "${propKey}"`)
        return target[propKey]
    }
  })
}
const object = { message: 'hello world' }
const wrapped = wrap(object)
console.log(wrapped.message)

Which outputs:

Reading property "message"
hello world

In this example we just do something before accessing the property / method. But then we return the original property or method.

You can also intercept changes to properties by implementing a set handler.

This could be useful to validate attributes or things like that. But I think this feature is a lot more promising. I hope new frameworks will arise that will use proxies for its core functionality. I’ve been thinking about it and these are some ideas:

🚀 An SDK for an API with 20 lines of code

As I said, you can intercept method calls for methods that… don’t even exist. When somebody calls a method on a proxied object the get handler will be called and then you can return a dynamically generated function. You don’t have to touch the proxied object if you don’t need to.

With that idea in mind, you can parse the method being invoked and dynamically implement its functionality in runtime! For example we could have a proxy that when invoked with api.getUsers() it could make a GET /users in an API. With this convention we can go further and api.postItems({ name: ‘Item name' }) would call POST /items with the first parameter as request body.

Let’s see a full implementation:

const { METHODS } = require('http')
const api = new Proxy({},
  {
    get(target, propKey) {
      const method = METHODS.find(method => 
        propKey.startsWith(method.toLowerCase()))
      if (!method) return
      const path =
        '/' +
        propKey
          .substring(method.length)
          .replace(/([a-z])([A-Z])/g, 'const { METHODS } = require('http')
const api = new Proxy({},
  {
    get(target, propKey) {
      const method = METHODS.find(method => 
        propKey.startsWith(method.toLowerCase()))
      if (!method) return
      const path =
        '/' +
        propKey
          .substring(method.length)
          .replace(/([a-z])([A-Z])/g, '$1/$2')
          .replace(/\$/g, '/$/')
          .toLowerCase()
      return (...args) => {
        const finalPath = path.replace(/\$/g, () => args.shift())
        const queryOrBody = args.shift() || {}
        // You could use fetch here
        // return fetch(finalPath, { method, body: queryOrBody })
        console.log(method, finalPath, queryOrBody)
      }
    }
  }
)
// GET /
api.get()
// GET /users
api.getUsers()
// GET /users/1234/likes
api.getUsers$Likes('1234')
// GET /users/1234/likes?page=2
api.getUsers$Likes('1234', { page: 2 })
// POST /items with body
api.postItems({ name: 'Item name' })
// api.foobar is not a function
api.foobar()
/$2')
          .replace(/\$/g, '/$/')
          .toLowerCase()
      return (...args) => {
        const finalPath = path.replace(/\$/g, () => args.shift())
        const queryOrBody = args.shift() || {}
        // You could use fetch here
        // return fetch(finalPath, { method, body: queryOrBody })
        console.log(method, finalPath, queryOrBody)
      }
    }
  }
)
// GET /
api.get()
// GET /users
api.getUsers()
// GET /users/1234/likes
api.getUsers$Likes('1234')
// GET /users/1234/likes?page=2
api.getUsers$Likes('1234', { page: 2 })
// POST /items with body
api.postItems({ name: 'Item name' })
// api.foobar is not a function
api.foobar()

Here the proxied object is just {} because all methods are dynamically implemented. We don’t actually need to wrap a functional object.

You’ll see that some methods have an ```There’s a very recent new feature of the JavaScript language that is still not being widely used: JavaScript proxies.

With JavaScript proxies you can wrap an existing object and intercept any access to its attributes or methods. Even if they do not exist! 💥

You can intercept calls to methods that do not exist

👋 Hello World JavaScript Proxy

Let’s start with the basics. A ‘hello world’ example could be:

const wrap = obj => {
  return new Proxy(obj, {
    get(target, propKey) {
        console.log(`Reading property "${propKey}"`)
        return target[propKey]
    }
  })
}
const object = { message: 'hello world' }
const wrapped = wrap(object)
console.log(wrapped.message)

Which outputs:

Reading property "message"
hello world

In this example we just do something before accessing the property / method. But then we return the original property or method.

You can also intercept changes to properties by implementing a set handler.

This could be useful to validate attributes or things like that. But I think this feature is a lot more promising. I hope new frameworks will arise that will use proxies for its core functionality. I’ve been thinking about it and these are some ideas:

🚀 An SDK for an API with 20 lines of code

As I said, you can intercept method calls for methods that… don’t even exist. When somebody calls a method on a proxied object the get handler will be called and then you can return a dynamically generated function. You don’t have to touch the proxied object if you don’t need to.

With that idea in mind, you can parse the method being invoked and dynamically implement its functionality in runtime! For example we could have a proxy that when invoked with api.getUsers() it could make a GET /users in an API. With this convention we can go further and api.postItems({ name: ‘Item name' }) would call POST /items with the first parameter as request body.

Let’s see a full implementation:

const { METHODS } = require('http')
const api = new Proxy({},
  {
    get(target, propKey) {
      const method = METHODS.find(method => 
        propKey.startsWith(method.toLowerCase()))
      if (!method) return
      const path =
        '/' +
        propKey
          .substring(method.length)
          .replace(/([a-z])([A-Z])/g, 'const { METHODS } = require('http')
const api = new Proxy({},
  {
    get(target, propKey) {
      const method = METHODS.find(method => 
        propKey.startsWith(method.toLowerCase()))
      if (!method) return
      const path =
        '/' +
        propKey
          .substring(method.length)
          .replace(/([a-z])([A-Z])/g, '$1/$2')
          .replace(/\$/g, '/$/')
          .toLowerCase()
      return (...args) => {
        const finalPath = path.replace(/\$/g, () => args.shift())
        const queryOrBody = args.shift() || {}
        // You could use fetch here
        // return fetch(finalPath, { method, body: queryOrBody })
        console.log(method, finalPath, queryOrBody)
      }
    }
  }
)
// GET /
api.get()
// GET /users
api.getUsers()
// GET /users/1234/likes
api.getUsers$Likes('1234')
// GET /users/1234/likes?page=2
api.getUsers$Likes('1234', { page: 2 })
// POST /items with body
api.postItems({ name: 'Item name' })
// api.foobar is not a function
api.foobar()
/$2')
          .replace(/\$/g, '/$/')
          .toLowerCase()
      return (...args) => {
        const finalPath = path.replace(/\$/g, () => args.shift())
        const queryOrBody = args.shift() || {}
        // You could use fetch here
        // return fetch(finalPath, { method, body: queryOrBody })
        console.log(method, finalPath, queryOrBody)
      }
    }
  }
)
// GET /
api.get()
// GET /users
api.getUsers()
// GET /users/1234/likes
api.getUsers$Likes('1234')
// GET /users/1234/likes?page=2
api.getUsers$Likes('1234', { page: 2 })
// POST /items with body
api.postItems({ name: 'Item name' })
// api.foobar is not a function
api.foobar()

Here the proxied object is just {} because all methods are dynamically implemented. We don’t actually need to wrap a functional object.

You’ll see that some methods have an `` This is a placeholder for inlined parameters.

If you don’t like that, it could be implemented in a different way. 🙂

Side note*: These examples can be optimized. You could cache the dynamically generated function in a hash object instead of returning a new function every time. But for clarity I left it like that for the examples.*

📦 Querying data structures with more readable methods

What if you had an array of people and you could do:

arr.findWhereNameEquals('Lily')
arr.findWhereSkillsIncludes('javascript')
arr.findWhereSkillsIsEmpty()
arr.findWhereAgeIsGreaterThan(40)

Sure you can with proxies! We can implement a proxy that wraps an array, parses method calls and does queries like that one.

I’ve implemented a few possibilities here:

const camelcase = require('camelcase')
const prefix = 'findWhere'
const assertions = {
  Equals: (object, value) => object === value,
  IsNull: (object, value) => object === null,
  IsUndefined: (object, value) => object === undefined,
  IsEmpty: (object, value) => object.length === 0,
  Includes: (object, value) => object.includes(value),
  IsLowerThan: (object, value) => object === value,
  IsGreaterThan: (object, value) => object === value
}
const assertionNames = Object.keys(assertions)
const wrap = arr => {
  return new Proxy(arr, {
    get(target, propKey) {
      if (propKey in target) return target[propKey]
      const assertionName = assertionNames.find(assertion =>
        propKey.endsWith(assertion))
      if (propKey.startsWith(prefix)) {
        const field = camelcase(
          propKey.substring(prefix.length,
            propKey.length - assertionName.length)
        )
        const assertion = assertions[assertionName]
        return value => {
          return target.find(item => assertion(item[field], value))
        }
      }
    }
  })
}
const arr = wrap([
  { name: 'John', age: 23, skills: ['mongodb'] },
  { name: 'Lily', age: 21, skills: ['redis'] },
  { name: 'Iris', age: 43, skills: ['python', 'javascript'] }
])
console.log(arr.findWhereNameEquals('Lily')) // finds Lily
console.log(arr.findWhereSkillsIncludes('javascript')) // finds Iris

It would be super similar to write an assertion library like expect using proxies.

Another idea would be to create a library to query databases with an API like this:

const id = await db.insertUserReturningId(userInfo)
// Runs an INSERT INTO user ... RETURNING id

📊 Monitoring async functions

Since you can intercept method calls, if a method call returns a promise you can also track when the promised is fulfilled. With that idea I made a quick example of monitoring the async methods of an object and printing some statistics in the command line.

You have a service like the following one and with one method call you can wrap it:

const service = {
  callService() {
    return new Promise(resolve =>
      setTimeout(resolve, Math.random() * 50 + 50))
  }
}
const monitoredService = monitor(service)
monitoredService.callService() // we want to monitor this

This is a full example:

const logUpdate = require('log-update')
const asciichart = require('asciichart')
const chalk = require('chalk')
const Measured = require('measured')
const timer = new Measured.Timer()
const history = new Array(120)
history.fill(0)
const monitor = obj => {
  return new Proxy(obj, {
    get(target, propKey) {
      const origMethod = target[propKey]
      if (!origMethod) return
      return (...args) => {
        const stopwatch = timer.start()
        const result = origMethod.apply(this, args)
        return result.then(out => {
          const n = stopwatch.end()
          history.shift()
          history.push(n)
          return out
        })
      }
    }
  })
}
const service = {
  callService() {
    return new Promise(resolve =>
      setTimeout(resolve, Math.random() * 50 + 50))
  }
}
const monitoredService = monitor(service)
setInterval(() => {
  monitoredService.callService()
    .then(() => {
      const fields = ['min', 'max', 'sum', 'variance',
        'mean', 'count', 'median']
      const histogram = timer.toJSON().histogram
      const lines = [
        '',
        ...fields.map(field =>
          chalk.cyan(field) + ': ' +
          (histogram[field] || 0).toFixed(2))
      ]
      logUpdate(asciichart.plot(history, { height: 10 })
        + lines.join('\n'))
    })
    .catch(err => console.error(err))
}, 100)

JavaScript proxies are super powerful. ✨

They add a little overhead but on the flip side having the ability to dynamically implement methods at runtime by their name makes the code super elegant and readable. I haven’t done any benchmarks yet, but if you plan to use them in production I would do some performance testing first.

However, there’s no problem of using them on development, like the monitoring of async functions for debugging!

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!