infix-to-postfix-notation/src/PostfixNotationConverter.js

A wonderful tool which converts expressions in infix notation to postfix notation using recursion.

module.exports = (function () {

    "use strict";

    function PostfixNotationConverter() {}

    PostfixNotationConverter.prototype = {
        constructor: PostfixNotationConverter,

        convertToPostfixNotation: function (infixNotation) {

            if (infixNotation && infixNotation.length === 1) {

                if (+infixNotation) {
                    return infixNotation;
                } else {
                    return "";
                }

            } else {
                var postfixNotation = "",
                    crtChar = infixNotation.charAt(0),
                    indexOfCrtChar = infixNotation.indexOf(crtChar);

                if (+crtChar) {
                    postfixNotation = crtChar + this.convertToPostfixNotation(infixNotation.substring(indexOfCrtChar + 1,
                        infixNotation.length));

                } else if (/(\+|-|\*|\/|<|>|<\=|>\=|\=\=|\=\=\=|\!\=|\!\=\=|&&|\|\|)/.test(crtChar)) {
                    var nextChar = infixNotation.charAt(indexOfCrtChar + 1),
                        indexOfNextChar = infixNotation.indexOf(nextChar);

                    if (nextChar === "(") {
                        var indexOfClosingParenthesis = getIndexOfClosingParenthesis(indexOfNextChar, infixNotation);

                        postfixNotation = this.convertToPostfixNotation(
                            infixNotation.substring(indexOfNextChar, indexOfClosingParenthesis + 1)) + crtChar + this.convertToPostfixNotation(
                            infixNotation.substring(indexOfClosingParenthesis + 1, infixNotation.length));

                    } else {
                        var indexOfLastDigit = getIndexOfLastDigit(indexOfNextChar, infixNotation);
                        postfixNotation = this.convertToPostfixNotation(
                                infixNotation.substring(indexOfNextChar, indexOfLastDigit + 1)) + crtChar +
                            this.convertToPostfixNotation(
                                infixNotation.substring(indexOfLastDigit + 1, infixNotation.length));
                    }

                } else if (crtChar === "(" || crtChar === ")") {
                    postfixNotation = this.convertToPostfixNotation(infixNotation.substring(indexOfCrtChar + 1, infixNotation.length));
                }

                return postfixNotation;
            }
        }
    };

    // TODO: Improve?
    function getIndexOfLastDigit(indexOfFirstDigit, infixNotation) {
        var indexOfLastDigit = -1,
            index = indexOfFirstDigit,
            crtDigit = infixNotation.charAt(index);

        while (+crtDigit && index < infixNotation.length) {
            indexOfLastDigit = index;
            crtDigit = infixNotation.charAt(++index);
        }

        return indexOfLastDigit;
    }

    function getIndexOfClosingParenthesis(indexOfOpenParenthesis, infixNotation) {
        var indexOfClosingParenthesis = -1,
            numberOfOpenParentheses = 1; // The current open parenthesis.

        for (var i = indexOfOpenParenthesis + 1, j = infixNotation.length; i < j; i++) {
            var crtChar = infixNotation.charAt(i);
            numberOfOpenParentheses += (crtChar === "(") ? 1 : (crtChar === ")") ? -1 : 0;

            if (numberOfOpenParentheses === 0) {
                indexOfClosingParenthesis = i;
                break;
            }
        }

        return indexOfClosingParenthesis;
    }

    return new PostfixNotationConverter(); // To mimic an utility class.

})();