JS await only valid in async function. How to resolve?

Question

Can anyone please tell me I defined a function as async but still it not working and throwing error How can I resolve this issue?

 var courses = [ {ID: 1, Name: 'course 1', Author: 'Mariela Mckinney', Website: 'www.loarpharei.com'}, {ID: 2, Name: 'course 2', Author: 'Brylee Becker', Website: 'www.phattiodye.com'}, {ID: 3, Name: 'course 3', Author: 'Weston Edwards', Website: 'www.pretathlew.com'}, {ID: 4, Name: 'course 4', Author: 'Nathanael Fox', Website: 'www.senfredral.com'}, {ID: 5, Name: 'course 5', Author: 'Aarav Park', Website: 'www.ebreanerin.com'} ] async function get_course(ID){ return setTimeout(function(){ console.log('I am fired'); return get_index(ID); }, 2000); } let course_id = await get_course(2); console.log(course_id);

Answer 1

There are many mistakes in the code. I hope the snippet helps you.

 const courses = [ {id: 1, name: 'course 1', author: 'Mariela Mckinney', website: 'www.loarpharei.com'}, {id: 2, name: 'course 2', author: 'Brylee Becker', website: 'www.phattiodye.com'}, {id: 3, name: 'course 3', author: 'Weston Edwards', website: 'www.pretathlew.com'}, {id: 4, name: 'course 4', author: 'Nathanael Fox', website: 'www.senfredral.com'}, {id: 5, name: 'course 5', author: 'Aarav Park', website: 'www.ebreanerin.com'}, ] // The "async" keyword is actually redundant if there is no "await" keyword in // the function. async function getCourse(id) { return new Promise((resolve) => { setTimeout(() => { console.log('I am fired'); resolve(courses[id]); }, 2000); }); } async function main() { // You can always "await" an Async function, or a function returning a Promise. const course = await getCourse(2); console.log(course); } main(); // Notes: // 1. Always use camelCase for field names, function names and variable names. // 2. Most JavaScript developers prefer 2-space indent, instead of 4.

Answer 2

You cannot use await outside of an async function. It is how the API is designed. See the docs at https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/await :

The await operator is used to wait for a Promise. It can only be used inside an async function.

If you want to use await you need to wrap

let course_id = await get_course(2);

inside an async function.

Also, as Daniel A. White pointed out, setTimeout doesn't return a Promise , but a timer ID that you can later use to cancel the timeout.

Answer 3

You could use IIFE to wrap your await call in async function but you also need return promise from other function.

 var courses = [{ID: 1, Name: 'course 1', Author: 'Mariela Mckinney', Website: 'www.loarpharei.com'},{ID: 2, Name: 'course 2', Author: 'Brylee Becker', Website: 'www.phattiodye.com'},{ID: 3, Name: 'course 3', Author: 'Weston Edwards', Website: 'www.pretathlew.com'},{ID: 4, Name: 'course 4', Author: 'Nathanael Fox', Website: 'www.senfredral.com'},{ID: 5, Name: 'course 5', Author: 'Aarav Park', Website: 'www.ebreanerin.com'}] function get_course(ID) { console.log('I am fired.') return new Promise(resolve => { setTimeout(() => { resolve(courses) }, 2000) }) } (async() => { let course_id = await get_course(2); console.log(course_id); })()

Answer 4

setTimeout doesn't return a promise. You have to wrap it in a new Promise(...) call. The get_course(2) call is just a free/floating call that isn't inside of any function, so await wont work there.

Answer 5

You should wrap you setTimeout into Promise. see the example:

 (async() => {var courses = [ {ID: 1, Name: 'course 1', Author: 'Mariela Mckinney', Website: 'www.loarpharei.com'}, {ID: 2, Name: 'course 2', Author: 'Brylee Becker', Website: 'www.phattiodye.com'}, {ID: 3, Name: 'course 3', Author: 'Weston Edwards', Website: 'www.pretathlew.com'}, {ID: 4, Name: 'course 4', Author: 'Nathanael Fox', Website: 'www.senfredral.com'}, {ID: 5, Name: 'course 5', Author: 'Aarav Park', Website: 'www.ebreanerin.com'} ] function get_index(id) { return courses.findIndex(i => i.ID === id); } function get_course(ID){ return new Promise(resolve => { setTimeout(function(){ console.log('I am fired'); resolve(get_index(ID)); }, 2000); }); } let course_id = await get_course(2); console.log(course_id); })();