JavaScript/Promise.html at master · vishal-vaish/JavaScript · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

</body>
</html>
<script>
    const cart=["shoes","pants","kurta"];
    function validateCart(){
        return true;
    }

    function proceedToPayment(orderId){
        return new Promise(function(resolve,reject){
            if(!orderId){
                reject(new Error("Order Id is required"));
            }

            setTimeout(()=>{
                resolve("Payment Successful");
            },3000);
        })
    }
    function createOrder(){
        //to create a Promise use a promise constructor and pass it a callback
        const pr= new Promise(function(resolve,reject){
            //resolve and reject are both function
            //resolve take the promise to fullfilled state
            //reject take the promise to rejected state
            if(!validateCart()){
                reject(new Error("Cart is not valid"));
            }else{
                const orderId="12345";
                //it will take the ptomise to fullfilled state
                //In resolve you can pass any data
                resolve(orderId);
            }
        })

        return pr;
    }
//create order function return a promise
// A Promise can be know if a promise is completed or not with a signal called then

createOrder().then(function(data){
    //if resolve
    console.log("orderId is:",data);
    //In order to give data to next then you need to return it
    return data;
}).then((previousThenData)=>{
    //this then will receive the data from immediately previous then
    return
    proceedToPayment(previousThenData);
}).then((paymentData)=>{
    console.log("Payment Data is:",paymentData);
}).catch(err=>{
    console.log("Error is:",err.message);
})


</script>