【JS基础】手写Promise.all

我还以为是先手写promise，再实现all方法呢，没想到这么简单。。。

/**
 * 手写 promise.all
 */
function promiseAll(args) {
    return new Promise((resolve, reject) => {
        const promiseResult = []
        let iteratorIndex = 0
        let fullCount = 0
        for(const item of args) {
            let resultIndex = iteratorIndex;
            iteratorIndex += 1
            Promise.resolve(item).then(res => {
                promiseResult[resultIndex] = res
                fullCount += 1
                if(fullCount === args.length) {
                    resolve(promiseResult)
                }
            }).catch(err => {
                reject(err)
            })
        }

        if(iteratorIndex === 0) {
            resolve(promiseResult)
        }
    })
}

if(!Promise.all) {
    Promise.all = promiseAll
}


const p1 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(1)
    }, 1000)
})


const p2 = new Promise((resolve, reject) => {
    setTimeout(() => {
        resolve(2)
    }, 2000)
})

const p3 = new Promise((resolve, reject) => {
    setTimeout(() => {
        // resolve(3)
        reject(3)
    }, 3000)
})

promiseAll([p1, p2, p3]).then(res => {
    console.log(res)
}).catch(err => {
    console.error('err: ', err)
}).finally(() => {
    console.log('finally')
})