Typescript conversion to boolean

Question

In Typescript I can do this:

var xxx : some_type;

if (xxx)
    foo();
else
    bar();

Here xxx will be treated as a boolean, regardless of its

Answer 1

Here's a simple function that will handle most scenarios, including handling booleans as an input (just in case):

type Falsey = undefined | null;
const parseBoolean = (val: string | boolean | number | Falsey): boolean => {
  const s = val && val.toString().toLowerCase().trim();
  if (s == 'true' || s == '1')
    return true;
  return false; 
}

And here's a jest test to go with it:

describe('Boolean Parser', () => {
    [
        { val: 'true', expected: true },
        { val: 'false', expected: false },
        { val: 'True', expected: true },
        { val: 'False', expected: false },
        { val: 'TRUE', expected: true },
        { val: 'FALSE', expected: false },
        { val: '', expected: false },
        { val: '1', expected: true },
        { val: '0', expected: false },
        { val: false, expected: false },
        { val: true, expected: true },
        { val: undefined, expected: false },
        { val: null, expected: false },
        { val: 0, expected: false },
        { val: 1, expected: true },
        { val: 111, expected: false }
    ].forEach(args => {
        it(`should parse ${args.val} to boolean`, () => {
            expect(parseBoolean(args.val)).toBe(args.expected);
        });
    })
});