JavaScript - convert longitude and latitude from degrees, minutes, and seconds (DMS) to decimal degrees (DD)

const SPACE_EXPRESSION = /\s+/;

​

const LATITUDE_EXPRESSION = /^(\d{1,2})°(?:\s*(\d{1,2})[′'])?\s*(N|S|N\/S)$/;  // 0- 90° 0-59′ N/S

const LONGITUDE_EXPRESSION = /^(\d{1,3})°(?:\s*(\d{1,2})[′'])?\s*(E|W|E\/W)$/; // 0-180° 0-59′ E/W

​

const matchText = (expression, text) => {

    expression.lastIndex = 0;

    return expression.exec(text);

};

​

const parseCordinate = (expression, limit, surfaces, text) => {

    const match = matchText(expression, text);

    if (match) {

        const degrees = parseInt(match[1]); // 0-90° or 0-180°

        if (degrees > limit) {

            throw new Error('Incorrect degrees value (should be in range from 0 to ' + limit + ').');

        }

        const minutes = parseInt(match[2] || '0'); // 0-59′

        if (minutes > 59) {

            throw new Error('Incorrect minutes value (should be in range from 0 to 59).');

        }

        if (degrees === 0 && minutes === 0) {

            return 0;

        }

        const surface = match[3]; // N/S or E/W

        switch (surface) {

            case surfaces[0]: return +(degrees + minutes / 60);

            case surfaces[1]: return -(degrees + minutes / 60);

            default:

                throw new Error('Incorrect surface value (should be ' + surfaces[0] + ' or ' + surfaces[1] + ').');

        }

    }

    throw new Error('Incorrect cordinate format.');

};

​

const parseLatitude = (latitude) => parseCordinate(LATITUDE_EXPRESSION, 90, 'NS', latitude);

const parseLongitude = (longitude) => parseCordinate(LONGITUDE_EXPRESSION, 180, 'EW', longitude);

​

const parsePosition = (position) => {

    if (position) {

        const parts = position.split(SPACE_EXPRESSION);

        if (parts.length === 2) {

            const latitude = parseLatitude(parts[0]);

            const longitude = parseLongitude(parts[1]);

            return {latitude, longitude};

        }

    }

    return new Error('Incorrect position format.');

};

​

​

// Usage example:

​

// 51°53′N 176°39′W ---> 51.88333 -176.65

//

const latitude = parseLatitude('51°53′N');           //   51.88333

const longitude = parseLongitude('176°39′W');        // -176.65

​

const position = parsePosition('51°53′N 176°39′W');  // 51.88333 -176.65

​

console.log(latitude);                  //   51.88333

console.log(longitude);                 // -176.65

console.log(JSON.stringify(position));  // {"latitude":51.88333333333333,"longitude":-176.65}