考查知识点
- 理解JS是一门单线程语言；
- 理解宏任务和微任务相关；
微任务队列
- promise
- MutationObserver
- process.nexTick
- async;await
宏任务队列
- setTimeout
- setInterval
- UI rending
- script
第一题
console.log('script start')
async function async1() {
await async2()
console.log('async1 end')
}
async function async2() {
console.log('async2 end')
}
async1()
setTimeout(function() {
console.log('setTimeout')
}, 0)
new Promise(resolve => {
console.log('Promise')
resolve()
})
.then(function() {
console.log('promise1')
})
.then(function() {
console.log('promise2')
})
console.log('script end')
执行结果：
- script start
- async2 end
- Promise
- script end
- async1 end
- promise1
- promise2
- setTimeout
第二题
async function async1() {
console.log( 'async1 start' )
await async2()
console.log( 'async1 end' )
}
async function async2() {
console.log( 'async2' )
}
console.log( 'script start' )
setTimeout( function () {
console.log( 'setTimeout' )
}, 0 )
async1();
new Promise( function ( resolve ) {
console.log( 'promise1' )
resolve();
} ).then( function () {
console.log( 'promise2' )
} )
console.log( 'script end' )
执行结果：
- script start
- async1 start
- async2 promise1
- script end
- async1 end
- promise2
- setTimeout
