Test for array of string type in TypeScript

How can I test if a variable is an array of string in TypeScript? Something like this:

function f(): string {
    var a: string[] = ["A", "B", "C"];

    if (typeof a === "string[]")    {
        return "Yes"
    }
    else {
        // returns no as it's 'object'
        return "No"
    }
};

TypeScript.io here: http://typescript.io/k0ZiJzso0Qg/2

Edit: I've updated the text to ask for a test for string[]. This was only in the code example previously.

Solution 1:

You cannot test for string[] in the general case but you can test for Array quite easily the same as in JavaScript https://stackoverflow.com/a/767492/390330 (I prefer Array.isArray(value)).

If you specifically want for string array you can do something like:

if (Array.isArray(value)) {
   var somethingIsNotString = false;
   value.forEach(function(item){
      if(typeof item !== 'string'){
         somethingIsNotString = true;
      }
   })
   if(!somethingIsNotString && value.length > 0){
      console.log('string[]!');
   }
}

Solution 2:

Another option is Array.isArray()

if(! Array.isArray(classNames) ){
    classNames = [classNames]
}