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宏任务与微任务输出顺序练习题

news 2026/3/26 23:35:19

文章目录

- - 一.宏任务与微任务输出顺序练习题
  - - 第一题
    - 第二题
    - 第三题
    - 第四题
    - 第五题

一.宏任务与微任务输出顺序练习题

第一题

asyncfunctionfn(){console.log('fn start');awaitPromise.resolve();console.log('fn end');}console.log('script start');fn();setTimeout(()=>{console.log('setTimeout');},0);console.log('script end');

我的回答:script start,fn start,fn end,script end,setTimeout
参考答案：script start → fn start →script end → fn end→ setTimeout
注:async函数在调用时,先执行里面的同步部分,直到遇到await,会把后续代码放入微任务队列(fn end),因此后续的同步代码(‘script end’)会先执行

第二题

console.log('a');setImmediate(()=>{console.log('setImmediate1');});setTimeout(()=>{console.log('setTimeout1');},0);Promise.resolve().then(()=>{console.log('then1');setImmediate(()=>{console.log('setImmediate2');});});console.log('b');

我的回答:a b setImmediate1 then1 setImmediate2 setTimeout1
参考答案：a → b →then1 → setTimeout1 → setImmediate1 → setImmediate2
注:1.微任务(then1)>所有宏任务(setImmediate和setTimeout)
2.宏任务队列中，setTimeout（0ms）优先级高于 setImmediate

第三题

asyncfunctionasync1(){awaitasync2();console.log('async1 end');}asyncfunctionasync2(){console.log('async2');returnPromise.resolve('async2 resolve');}console.log('script start');async1();setTimeout(()=>{console.log('setTimeout');},0);Promise.resolve().then(()=>{console.log('promise then');});console.log('script end');

我的回答:script start,async2,async1 end,script end,promise then,async2 resolve,setTimeout
参考答案：script start → async2 →script end → async1 end → promise then→ setTimeout
注:’async2 resolve’不会输出,没有then
输出过程:

同步代码:script start → async2 → script end 其中,’async2’的输出过程是这样的:调用async1()=>进入async1函数=>执行awaitasync2()=>同步调用async2函数=>进入async2函数=>输出’async2’微任务:async1end=>promise then宏任务:setTimeout

第四题

console.log('1');setTimeout(()=>{console.log('2');},100);setTimeout(()=>{console.log('3');},0);Promise.resolve().then(()=>{console.log('4');});console.log('5');

输出顺序:1 5 4 2 3
参考答案：1 → 5 → 4 → 3 → 2
注:setTimeout（0ms）比 setTimeout（100ms）先执行

第五题

process.nextTick(()=>{console.log('nextTick1');});console.log('start');setTimeout(()=>{console.log('setTimeout');process.nextTick(()=>{console.log('nextTick2');});},0);Promise.resolve().then(()=>{console.log('promise');});process.nextTick(()=>{console.log('nextTick3');});console.log('end');