在Angular 7中检查未定义的失败

Question

我正在尝试对Angular 7中的数字变量进行未定义的检查。尽管该值未定义，但它不满足条件。你能告诉我我要去哪里了吗？

public init(val: string, selectedClassficationId: number) {
        this.Mode = val;
        if (selectedClassficationId !== undefined) {
        this.getClassificationDetails(selectedClassficationId);
        }
    }

Answer 1

为什么不尝试这个？

如果selectedClassficationId的值为undefined，null，false，0，则不会执行if块。

if (selectedClassficationId || selectedClassficationId == 0) {
  this.getClassificationDetails(selectedClassficationId);
}
else {
  console.log('The value is either undefined, null, false, 0', selectedClassficationId);
}

Here是每个用例的详细示例：

Answer 2

您可以尝试

public init(val: string, selectedClassficationId: number) {
        this.Mode = val;
        if (selectedClassficationId != null) { // != null is check null as well as undefine at the same time 
        this.getClassificationDetails(selectedClassficationId);
        }
    }

我希望它可以帮助您