Convert state name to abbreviation in JavaScript. There's some better solutions in the comments, so scroll down!

stateToAbbr.js

// There's some better solutions in the comments, so scroll down and see how other folks have improved this!

// USAGE:
// abbrState('ny', 'name');
// --> 'New York'
// abbrState('New York', 'abbr');
// --> 'NY'

function abbrState(input, to){
    
    var states = [
        ['Arizona', 'AZ'],
        ['Alabama', 'AL'],
        ['Alaska', 'AK'],
        ['Arkansas', 'AR'],
        ['California', 'CA'],
        ['Colorado', 'CO'],
        ['Connecticut', 'CT'],
        ['Delaware', 'DE'],
        ['Florida', 'FL'],
        ['Georgia', 'GA'],
        ['Hawaii', 'HI'],
        ['Idaho', 'ID'],
        ['Illinois', 'IL'],
        ['Indiana', 'IN'],
        ['Iowa', 'IA'],
        ['Kansas', 'KS'],
        ['Kentucky', 'KY'],
        ['Louisiana', 'LA'],
        ['Maine', 'ME'],
        ['Maryland', 'MD'],
        ['Massachusetts', 'MA'],
        ['Michigan', 'MI'],
        ['Minnesota', 'MN'],
        ['Mississippi', 'MS'],
        ['Missouri', 'MO'],
        ['Montana', 'MT'],
        ['Nebraska', 'NE'],
        ['Nevada', 'NV'],
        ['New Hampshire', 'NH'],
        ['New Jersey', 'NJ'],
        ['New Mexico', 'NM'],
        ['New York', 'NY'],
        ['North Carolina', 'NC'],
        ['North Dakota', 'ND'],
        ['Ohio', 'OH'],
        ['Oklahoma', 'OK'],
        ['Oregon', 'OR'],
        ['Pennsylvania', 'PA'],
        ['Rhode Island', 'RI'],
        ['South Carolina', 'SC'],
        ['South Dakota', 'SD'],
        ['Tennessee', 'TN'],
        ['Texas', 'TX'],
        ['Utah', 'UT'],
        ['Vermont', 'VT'],
        ['Virginia', 'VA'],
        ['Washington', 'WA'],
        ['West Virginia', 'WV'],
        ['Wisconsin', 'WI'],
        ['Wyoming', 'WY'],
    ];

    if (to == 'abbr'){
        input = input.replace(/\w\S*/g, function(txt){return txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase();});
        for(i = 0; i < states.length; i++){
            if(states[i][0] == input){
                return(states[i][1]);
            }
        }    
    } else if (to == 'name'){
        input = input.toUpperCase();
        for(i = 0; i < states.length; i++){
            if(states[i][1] == input){
                return(states[i][0]);
            }
        }    
    }
}

another ts version:
/**

• Convert US state abbreviation to full name and vice-versa
• @param {string} input - input string to convert
  */
  export default function convertUsStateAbbrAndName(input: string): string | null {
  const toAbbr = input.length !== 2;

const states = [
['Alabama', 'AL'],
['Alaska', 'AK'],
['American Samoa', 'AS'],
['Arizona', 'AZ'],
['Arkansas', 'AR'],
['Armed Forces Americas', 'AA'],
['Armed Forces Europe', 'AE'],
['Armed Forces Pacific', 'AP'],
['California', 'CA'],
['Colorado', 'CO'],
['Connecticut', 'CT'],
['Delaware', 'DE'],
['District Of Columbia', 'DC'],
['Florida', 'FL'],
['Georgia', 'GA'],
['Guam', 'GU'],
['Hawaii', 'HI'],
['Idaho', 'ID'],
['Illinois', 'IL'],
['Indiana', 'IN'],
['Iowa', 'IA'],
['Kansas', 'KS'],
['Kentucky', 'KY'],
['Louisiana', 'LA'],
['Maine', 'ME'],
['Marshall Islands', 'MH'],
['Maryland', 'MD'],
['Massachusetts', 'MA'],
['Michigan', 'MI'],
['Minnesota', 'MN'],
['Mississippi', 'MS'],
['Missouri', 'MO'],
['Montana', 'MT'],
['Nebraska', 'NE'],
['Nevada', 'NV'],
['New Hampshire', 'NH'],
['New Jersey', 'NJ'],
['New Mexico', 'NM'],
['New York', 'NY'],
['North Carolina', 'NC'],
['North Dakota', 'ND'],
['Northern Mariana Islands', 'NP'],
['Ohio', 'OH'],
['Oklahoma', 'OK'],
['Oregon', 'OR'],
['Pennsylvania', 'PA'],
['Puerto Rico', 'PR'],
['Rhode Island', 'RI'],
['South Carolina', 'SC'],
['South Dakota', 'SD'],
['Tennessee', 'TN'],
['Texas', 'TX'],
['US Virgin Islands', 'VI'],
['Utah', 'UT'],
['Vermont', 'VT'],
['Virginia', 'VA'],
['Washington', 'WA'],
['West Virginia', 'WV'],
['Wisconsin', 'WI'],
['Wyoming', 'WY'],
];

// So happy that Canada and the US have distinct abbreviations
const provinces = [
['Alberta', 'AB'],
['British Columbia', 'BC'],
['Manitoba', 'MB'],
['New Brunswick', 'NB'],
['Newfoundland', 'NF'],
['Northwest Territory', 'NT'],
['Nova Scotia', 'NS'],
['Nunavut', 'NU'],
['Ontario', 'ON'],
['Prince Edward Island', 'PE'],
['Quebec', 'QC'],
['Saskatchewan', 'SK'],
['Yukon', 'YT'],
];

const regions = states.concat(provinces);

let i; // Reusable loop variable

if (toAbbr) {
input = input.replace(/\w\S*/g, function (txt: string) {
return txt.charAt(0).toUpperCase() + txt.substr(1).toLowerCase();
});
for (i = 0; i < regions.length; i++) {
if (regions[i][0] === input) {
return regions[i][1];
}
}
} else {
input = input.toUpperCase();
for (i = 0; i < regions.length; i++) {
if (regions[i][1] === input) {
return regions[i][0];
}
}
}

return null;
}

Thanks @davidteather, @nandorojo, @rinogo! Very helpful.

TWIMC - https://www.npmjs.com/package/us-state-converter

stateNameToAbbreviation.ts

export default function stateNameToAbbreviation(name: string): string {
    const lowerCaseAbbreviationKey = name.trim().replace(/[^\w ]/g, "").toLowerCase(); // Trim, lowercase and remove all non-word characters with the exception of spaces
    return states[lowerCaseAbbreviationKey] ?? name; // Return name if record is not found
}

const states: Record<string, string> = {
    "arizona": "AZ",
    "alabama": "AL",
    "alaska": "AK",
    "arkansas": "AR",
    "california": "CA",
    "colorado": "CO",
    "connecticut": "CT",
    "district of columbia": "DC",
    "delaware": "DE",
    "florida": "FL",
    "georgia": "GA",
    "hawaii": "HI",
    "idaho": "ID",
    "illinois": "IL",
    "indiana": "IN",
    "iowa": "IA",
    "kansas": "KS",
    "kentucky": "KY",
    "louisiana": "LA",
    "maine": "ME",
    "maryland": "MD",
    "massachusetts": "MA",
    "michigan": "MI",
    "minnesota": "MN",
    "mississippi": "MS",
    "missouri": "MO",
    "montana": "MT",
    "nebraska": "NE",
    "nevada": "NV",
    "new hampshire": "NH",
    "new jersey": "NJ",
    "new mexico": "NM",
    "new york": "NY",
    "north carolina": "NC",
    "north dakota": "ND",
    "ohio": "OH",
    "oklahoma": "OK",
    "oregon": "OR",
    "pennsylvania": "PA",
    "rhode island": "RI",
    "south carolina": "SC",
    "south dakota": "SD",
    "tennessee": "TN",
    "texas": "TX",
    "utah": "UT",
    "vermont": "VT",
    "virginia": "VA",
    "washington": "WA",
    "west virginia": "WV",
    "wisconsin": "WI",
    "wyoming": "WY",
    "american samoa": "AS",
    "guam": "GU",
    "northern mariana islands": "MP",
    "puerto rico": "PR",
    "us virgin islands": "VI",
    "us minor outlying islands": "UM",
};