Boolean() cannot be used to perform a null check

**TypeScript Version:** 2.4.0 Apologies for today's issue raising binge. **Code** ```ts // Compiles const nullCheckOne = (value?: number) => { if (!!value) { return value.toFixed(0); } return ''; } const nullCheckTwo = (value?: number) => { if (Boolean(value)) { // Object is possibly 'undefined' return value.toFixed(0); } return ''; } ``` **Expected behavior:** Both examples compile. **Actual behavior:** The latter example fails w/ `Object is possibly 'undefined'`. **Explanation** To my knowledge `!!value` and `Boolean(value)` are equivalent. I'm wondering what is the reason behind not supporting the second case. One reason I can think of would be an imported, non-typescript module, globally overriding it to something like: `Boolean = (value) => !value`.

Posted by kujon on Jun 20, 2017, 7:03 PM

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• github (Other)

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