throw-expression

This package emulates proposed functionality with inline throwable expression.

Before:

const length = (value: string) => {
    if (value === undefined || value === null) {
        throw new Error('falsy value entered!');
    }
    return value.length;
}

After:

const length = (value: string) => throwIfFalsy(value, 'falsy value entered!').length; // will not throw on empty string, zero etc.

// Or:

const length = (value: string) => (value || Throw('falsy value entered!')).length; // will throw on any falsy value

The function is named 'Throw' to avoid javascript keyword. Along with this function, several other simple utility functions are exported. Typing on these utilities should help you avoid most of the nonsensical TS messages about nullable properties.

Examples from unit tests

describe("Can use throwable expressions to throw when necessary", () => {
    test("Can simply throw", () => {
        expect(() => Throw('Write your exception message here')).toThrow('Write your exception message here');
        expect(() => Throw(Error('Write your exception message here'))).toThrow('Write your exception message here');        
    });
    test("Can throw conditionally", () => {
        let value: string | null = null;
        expect(() => value || Throw('is null')).toThrow('is null');
        value = 'anything else';
        expect(value || Throw('is null')).toBe('anything else');
    });
    test("Can check for null with throwable", () => {
        expect(() => throwIfNull(null, 'is null')).toThrow('is null');
        expect(throwIfNull(undefined, 'is null')).toBe(undefined);
        expect(throwIfNull(false, 'is null')).toBe(false);
    });
    test("Can check for undefined with throwable", () => {
        expect(throwIfUndefined(null, 'is undefined')).toBe(null);
        expect(() => throwIfUndefined(undefined, 'is undefined')).toThrow('is undefined');
        expect(throwIfUndefined(false, 'is undefined')).toBe(false);
    });
    test("Can check for falsy with throwable", () => {
        expect(() => throwIfFalsy(null, 'is falsy')).toThrow('is falsy');
        expect(() => throwIfFalsy(undefined, 'is falsy')).toThrow('is falsy');
        expect(() => throwIfFalsy("", 'is falsy')).toThrow('is falsy');
        expect(() => throwIfFalsy(0, 'is falsy')).toThrow('is falsy');
        expect(() => throwIfFalsy(NaN, 'is falsy')).toThrow('is falsy');
        expect(() => throwIfFalsy(false, 'is falsy')).toThrow('is falsy');
        expect(throwIfFalsy("is truthy", 'is falsy').length).toBe(9);
    });
    test("Can check for nullish with throwable", () => {
        expect(() => throwIfNullish(null, 'is nullish')).toThrow('is nullish');
        expect(() => throwIfNullish(undefined, 'is nullish')).toThrow('is nullish');
        expect(throwIfNullish("", 'is nullish')).toBe("");
        expect(throwIfNullish(false, 'is nullish')).toBe(false);
    });
    test("Can check for NaN with throwable", () => {
        expect(() => throwIfNotANumber(NaN, 'is NaN')).toThrow('is NaN');
        expect(() => throwIfNotANumber({}, 'is NaN')).toThrow('is NaN');
        expect(throwIfNotANumber(0, 'is NaN')).toBe(0);
        expect(throwIfNotANumber(2, 'is NaN')).toBe(2);
    });
});

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If you encounter any bugs, or have ideas for improvement, do not hesitate to add a task or a pull request.