How to apply a type guard for jQuery instance?

2018-06-30 02:03:20

I'm trying to apply a type guard for a variable which might be a jQuery instance. However, as JQuery is an interface from jquery.d.ts , I can't use it with instanceof . The following code doesn't seem to work, I guess because TS doesn't "know" that being an instance of jQuery means being "an instance" of JQuery interface.

var stringOrJQuery: string | JQuery;
...
if (stringOrJQuery instanceof jQuery) {
  ...
  // here stringOrJQuery is still string | JQuery
  ...
}

I'm using TS 2.0 beta.

You can check string case:

if(typeof stringOrJQuery === 'string') {
    // string case
}
else {
    // jquery case case
}

Alternately, you can determine jQuery object by indirect checks like the ones described in this question's answers, such as:

if(stringOrJQuery.jquery !== undefined) { ... // this is a jQuery object

the jquery field of the jQuery object contains jQuery version and should be defined.

链接地址: http://www.djcxy.com/p/83946.html

上一篇: 从选定的值中获取文本

下一篇: 如何应用jQuery实例的类型警卫？