CODEWITHSUNDEEP
jquerytypescript
Zoltán Tamási
Zoltán Tamási

Reputation: 12809

How to apply a type guard for jQuery instance?

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.

Upvotes: 3

Views: 221

Answers (1)

TSV
TSV

Reputation: 7641

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.

Upvotes: 4

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