Angular promise inside promise？

Question

我有一个这样的函数：

resulta = 0;
resultb = 0;
resultc = 0;
resultd = 0;
    
    var wait = new promise((resolve, reject) => {
        data.forEach((single,index,array) =>{
            if (single.a == '1'){this.resulta = '1'}
            else if (single.a=='2') {this.resultb = '2'}
            else if (single.a=='3'){this.resultc = '3'}
            else if (single.a=='4'){
                this.function(single.a).then(async (bs) => {
                    if (somecondition) {
                        await bs.forEach(b => {
                            this.ccount = 0;
                            if(condition === true){
                                this.c = 'yes';
                                this.ccount = this.ccount +1;                      
                            }
                        });
                    }
                    if(this.ccount > 0){
                        this.resultd = '4';
                    }
                    else {
                       this.resultd = 'N/A';
                    }
                }
            }
            if (index === array.length -1)resolve();
        });
    });
    wait.then(async()=>{
        console.log('count', this.count); // always is 0 but it should be something > 0
        console.log('resulta', this.resulta); // 1 as it should be
        console.log('resultb', this.resultb); // 2 as it should be
        console.log('resultc', this.resultc); // 3 as it should be
        console.log('resultd', this.resultd); // 0 and it should be or 4 or N/A
    });

所以这里的问题是，第一个foreach在第二个foreach之前结束，所以它解决了承诺，在结束第一个foreach之前，我如何等待第二个foreach (在最新的else if中)完成呢？

Answer 1

您正在考虑promises应该在forEach块中工作得很好。不，不是那样的。你必须确保你内心的承诺应该得到适当的回报。然后，您可以创建promises数组，并使用Promise.all检查所有promises是否都已完成。

代码

const promises = data.map((single,index,array) =>{
    if (single.a == '1'){ return this.resulta = '1' }
    else if (single.a=='2') {return this.resultb = '2' }
    else if (single.a=='3'){ return this.resultc = '3' }
    else if (single.a=='4') {
        return this.function(single.a).then((bs) => {
            if (somecondition) {
                bs.forEach(b => {
                    this.ccount = 0;
                    if(condition === true){
                        this.c = 'yes';
                        this.ccount = this.ccount +1;                      
                    }
                });
            }
            if(this.ccount > 0){
                this.resultd = '4';
            }
            else {
               this.resultd = 'N/A';
            }
        }
    }
});

Promise.all(promises).then(async()=>{
    console.log('count', this.count);
    console.log('resulta', this.resulta);
    console.log('resultb', this.resultb);
    console.log('resultc', this.resultc);
    console.log('resultd', this.resultd);
});