What is the difference between the await keyword and the yield keyword?
Apr 23, 2022
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await keyword :
use the await keyword in an expression so, the async function execution will get paused until the promise is settled (that is, fulfilled or rejected), and to resume execution of the async function after fulfilment. When resumed, the value of the await expression is that of the fulfilled Promise.
await Ex:
<script>
function calculate(y) {
var promise = new Promise(function(resolve, reject) {
setTimeout(function() {
resolve(calculateSquare(y));
}, 3000);
});
return promise;
}
function calculateSquare(y) {
return y * y;
}
async function main() {
var s1 = await calculate(5);
//After 3 sec this line will get execute
console.log("Square of 5 is : " + s1);
var s2 = await calculate(10);
// After 3 sec next this line will get execute
console.log("Square of 10 is : " + s2);
// In last this line will get execute
console.log("End");
}
</script>
yield keyword :
yield keyword is used to pause the generator function execution, and the final value of the expression will be the value followed by the yield keyword is returned to the generator’s caller.
yield Ex :
<script>
function getValues(start, end) {
while (start <= end) {
yield start;
start++;
}
}
/* Expression */
var it = getValues(5, 10);
//element : {value : Object ,done : boolean}
var element = it.next();
while (element.done == false) {
console.log(element);
element = it.next();
}
// value:undefined, and done : false
console.log(element);
// because element.done == true
</script>
