如何知道formbuilder angular2中哪个字段发生了变化

Question

如何知道表单构建器angular2中哪个字段发生了变化， 我想添加一些检查，如果字段a是更改，那么如果字段b是更改，请执行此操作

this.comparisonForm = this.formBuilder.group({
        city: ['', [Validators.required]],
        brand: ['', [Validators.required]],
        productTemplate: ['', [Validators.required]],
        productAttributeValue: ['', [Validators.required]],
    });

this.comparisonForm.valueChanges
    .debounceTime(500)
    .subscribe(keyword => 
        console.log(keyword));

Answer 1

我遇到了同样的问题并最终订阅了每个字段。

this.comparisonForm['city']
.valueChanges 
.debounceTime(500)
.subscribe(value => console.log(value));