General Slugify function. Trim white-space. Replace all non-alphanumeric with dashes. Replace diacritics with generics Reduce chains of dashes to a single dash.

slugify.test.ts

describe("slugify()", () => {
    it("Must remove url encodings.", () => {
        const result = slugify("New%20York, NY");
        expect(result).toBe("new-york-ny");
    });
    
    it("Must replace non-alphanumerics with dashes.", () => {
        const result = slugify("a@b");
        expect(result).toBe("a-b");
    });

    it("Must trim all whitespace.", () => {
        const result = slugify("  ab  \r\n");
        expect(result).toBe("ab");
    });

    it("Must never include adjacent dashes.", () => {
        const result = slugify("New-York, \nNY");
        expect(result).toBe("new-york-ny");
    });

    it("Must return all alphas as lower case.", () => {
        const result = slugify("Amazon, TX");
        expect(result).toBe("amazon-tx");
    });

    it("Must convert diacritics to common characters.", () => {
        const result = slugify("Cañon City, Co");
        expect(result).toBe("canon-city-co");
    });
});

slugify.ts

/**
 * Convert a string to a slug.
 */
const slugify = (text: string): string => {
    const from: string = "àáäâèéëêìíïîòóöôùúüûñç"; // diacritic
    const to: string = "aaaaeeeeiiiioooouuuunc"; // generic

    let result: string = decodeURIComponent(text) // Remvoe URL encoding
        .trim() // remove leading and trailing whitespace
        .toLowerCase(); // convert to lower case

    from.split("").forEach((x, i) => {
        result = result.replace(new RegExp(x, "g"), to.charAt(i)); // replace diacritic
    });

    result = result
        .replace(/[^a-z0-9]/gmi, "-") // replace non-alphanumeric chars with -
        .replace(/-+/g, "-"); // collapse dashes

    return result;
};