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So finally, I'm back to my Visual Studio Code editor, and you can see I create a HTML file name index

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dot HTML.

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And I also open this file in my browser using live server extension inside the head tag.

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First I'm going to type script tag and inside the script tag.

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First I'm going to take a variable late complete and its value is true.

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It's a boolean value and I'm going to check this value in our promise method.

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We will do our next code depending on this result.

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Then I'm going to create a promise method.

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So I'm going to take a variable named Pro.

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And then I'm going to use new keyword new promise.

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And inside this promise method we have to create a function and I type function keyword.

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Then inside the curly braces we need to create conditions.

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So I'm going to create if condition.

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If inside the parentheses I am going to check our variable value.

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So I type my variable name complete.

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If true it redirect to if condition and if false then it redirect to else condition.

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As I told you before, promise return only to result it's return reject or fulfill.

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For this we need to take two parameter in our function.

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For successful.

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I am going to take result variable and for reject I'm going to take reject variable.

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If our function is satisfied then inside the if condition I'm going to use resolve function and if reject

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insert the else condition I'm going to call reject function.

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We don't need to create this function, we just need to call this function.

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If we call this function then we can use our inbuilt functions which is then and catch.

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And now I'm going to send message for resolve condition.

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I am successful for reject.

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I am going to send another message.

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I am failed and now I am going to call this Pro object in our console.

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Console dot log inside the round Braces Pro.

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It's not a normal function, it's an object.

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So we don't need to use round braces after object name.

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And if I save this file you can see in my console section you can see in my console it print.

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I am successful because we sent true value in our complete variable.

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And if I open it you can see promise result.

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I am successful and promise state fulfilled.

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But if I set false value to our variable and save this file, you can see a message I am failed and

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also it's showing an error.

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And if I open this promise, you can see promise state rejected.

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Also we can send parameter like normal function.

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So I'm going to remove this complete variable value.

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And I'm going to create a function function pro inside the round braces complete.

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Then inside the curly braces.

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And I'm going to move this code inside the curly braces.

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So our function going to return promise.

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So for now we don't need to take variables.

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So I'm going to remove this variable name and return new promise.

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And we need to pass value when we call this function.

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If I send true as an argument if I save this file you can see in my console it print I am successful.

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And if I send false as an argument now it's print I am failed.

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So our promise function worked properly.

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And now I'm going to create two different functions for resolve and for reject.

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For resolve I'm going to create a variable for late on fulfillment.

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And I'm going to use arrow function.

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And when we call this function I'm going to send a value which is result.

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And this value came from resolve function inside the curly braces console dot log result.

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Similarly we need to create another function for reject section.

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So I duplicate this lines and replace on fulfillment with on rejection and send error as in parameter

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console dot log print error.

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And as I told you before, we need to use callback function to call this functions which are then end

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catch.

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But first we need to call pro function.

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And inside the parentheses we need to send a value and our value is true dot.

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Then if our.

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Problem is resolved inside the parentheses.

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We need to call on fulfillment function.

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And I'm going to duplicate this line for rejection purpose.

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And this time we need to use catch function.

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And inside the parentheses we need to call on rejection function.

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And for now I don't need this console.log section.

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So I'm going to remove it.

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If I save this file you can see in my console it print I am successful.

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As I told you, promise has three stages.

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First one is pending, then resolve and reject.

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Let's talk about pending.

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We use it before promise start.

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So when I return the function inside the function first I'm going to type console dot log.

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Please wait.

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Now it is on pending stage.

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And then I'm going to use set timeout function.

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Set timeout.

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And then I'm going to create arrow function.

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I made a little mistake.

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We have to write the pending stage inside the promise function.

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So I am going to select this section and move it inside the promise method inside the set timeout section.

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I'm going to pass this if condition.

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And I want to pass this condition for 4000 milliseconds.

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And if I save this file you can see in my console first it print.

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Please wait.

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And we need to wait for four second but then it print I am successful.

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It print.

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Please wait twice to resolve this problem.

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I am going to use method chaining and make it.

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Then in catch function one liner I am going to remove this catch function.

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And after unfulfilment dot catch on rejection.

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Now if result is true, it is called all fulfillment function and if false it call on rejection function.

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And if I save this file you can see in my console section.

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First it print.

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Please wait.

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So we need to wait for four second, then it print.

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I am successful and similarly if I pass false parameter and save this file, we need to wait for four

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second.

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And then it print I am failed.

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Please.

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What is our pending message?

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We use a timeout function because it is take a long time to came data from the server.

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Let me show you one thing.

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If you do not want to create this function, you can.

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In that case, you directly call this function in then or catch section.

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So I'm going to copy this result function and call it inside the then function.

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And similarly I call error function in our catch function.

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And I'm going to comment out this previous line.

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And if I save this file first it run our pending stage.

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Then it print.

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I am failed because we send false value to our Pro function.

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Not only that we can pass multiple argument to our Pro function.

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For now, I don't need this line, so I'm going to remove it.

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And inside my pro function I am going to pass two parameter.

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Two and seven.

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And inside my function I'm going to take two parameters x and y.

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Then inside the promise I'm going to take another variable z.

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Z equal to x.

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Multiply by y.

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Then insert the set timeout function.

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If complete variable, replace with z.

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If multiplication is possible, then insert the result function.

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I'm going to use template string method inside the Backticks your result colon dollar sign inside the

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curly braces.

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Z means our result.

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Similarly, inside the reject function I'm going to send wrong input.

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If I save this file first we need to wait for four second.

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Then it print our result 14 because we pass two numeric value.

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So our condition is true.

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But if we pass a string value then what happened.

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So I'm going to pass a string value as an argument seven replace with small t.

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And if I save this file now you can see in my console it's print wrong input.

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Basically we handle errors using promise method.

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I hope now you understand what is promise in advanced JavaScript and why and how we use it.

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Thanks for watching this video.

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See you on the next tutorial.