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javascript async/await vs Promise
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| // Both these pieces of code produce the same output, but the async method is neater, because | |
| // all the variables stay in scope, and we can use a return statement to end the execution | |
| // at any point. | |
| // Here is the output in both cases: | |
| // f has been called with param 2 | |
| // ... | |
| // The quotient is 5 | |
| // f has been called with param -1 | |
| // Dividing by 1 is not interesting | |
| // f has been called with param -2 | |
| // Error: Attempt to divide by 0 | |
| // at f (index.js:...) | |
| // async | |
| // ----- | |
| const sleep = async (ms) => new Promise(resolve => setTimeout(resolve, ms)); | |
| const getDivisor = async (offset) => 2 + offset; | |
| const f = async (param) => { | |
| console.log(`f has been called with param ${param}`); | |
| try { | |
| const divisor = await getDivisor(param); | |
| if (divisor === 0) { | |
| throw new Error('Attempt to divide by 0'); | |
| } | |
| if (divisor === 1) { | |
| console.log('Dividing by 1 is not interesting'); | |
| return; | |
| } | |
| console.log('...'); | |
| await sleep(1000); | |
| const quotient = 20 / divisor; | |
| console.log(`The quotient is ${quotient}`); | |
| } catch (err) { | |
| console.log(err); | |
| } | |
| } | |
| (async () => { | |
| await f(2); | |
| await f(-1); | |
| f(-2); | |
| })(); | |
| // promise | |
| // ------- | |
| const sleep = async (ms) => new Promise(resolve => setTimeout(resolve, ms)); | |
| const getDivisor = async (offset) => 2 + offset; | |
| const f = (param) => { | |
| console.log(`f has been called with param ${param}`); | |
| return getDivisor(param).then(divisor => { | |
| if (divisor === 0) { | |
| throw new Error('Attempt to divide by 0'); | |
| } | |
| if (divisor === 1) { | |
| console.log('Dividing by 1 is not interesting'); | |
| return; | |
| } | |
| console.log('...'); | |
| return sleep(1000).then(() => divisor); | |
| }).then(divisor => { | |
| if (divisor === undefined) { | |
| return; | |
| } | |
| const quotient = 20 / divisor; | |
| console.log(`The quotient is ${quotient}`); | |
| }).catch(err => { | |
| console.log(err); | |
| }); | |
| } | |
| (async () => { | |
| await f(2); | |
| await f(-1); | |
| f(-2); | |
| })(); |
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