Typescript - object is possibly null

Question

I am creating simple function to count all existing vowels in given string. I wrote function to do it but I cannot compile this with Typescript version higher than 3. I am curious how this function should be written to pass Typescript versions higher than 3.

function getCount(str: string = ''): number {
      return str.match(/[aeiou]/gi).length;
    }

test:

describe("getCount", function(){
    it ("should pass a sample test", function(){
        assert.strictEqual(getCount("abracadabra"), 5)
    });
});

With Typescript version 2.4 everything passes but with higher versions I am getting this:

error TS2531: Object is possibly 'null'.

It seems strange to give a default value to the str , since you're counting the number of vowels in a string, the string should be required? Maybe consider removing the initial value — Alex Profir
– Alex Profir, Commented Feb 1, 2022 at 17:53

Raffael · Accepted Answer · 2022-02-01 17:52:35Z

1

This is because .match() will return null if there is no match found.

If it is null then length cannot be used. You could save the outcome of str.match(/[aeiou]/gi) to a variable and then check it is not null. The resulting function could look like this:

function getCount(str: string = ''): number {
  let matched = str.match(/[aeiou]/gi);
  if(matched) return matched.length;
  else return 0;
}

Look here to find more about match.

answered Feb 1, 2022 at 17:52

Raffael

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1 Comment

Freestyle09 Over a year ago

Yeah I saw that too, thanks for your answer!

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