Handy Grammar functions

GrammarUtil.ts

////////////////////////////////////////////////////////////////////////////////
//  Copyright(C) 2018 David Hamiter
////////////////////////////////////////////////////////////////////////////////
'use strict';

/**
* @author David Hamiter
* Static class for grammar checking
*/
abstract class GrammarUtil {
    //----------------------------------------------------------------------
    //
    //  Properties
    //
    //----------------------------------------------------------------------

    static readonly NUM_SUFFIX: string[] = ["th", "st", "nd", "rd", "th", "th", "th", "th", "th", "th"];

    private static readonly VOWEL_ARRAY: string[] = ["a", "e", "i", "o", "u", "8"];
    private static readonly PUNCTUATION_ARRAY: string[] = [".", "!", "?"];

    //----------------------------------------------------------------------
    //
    //  Constructor
    //
    //----------------------------------------------------------------------

    private constructor() { } // Static class cannot be instantiated

    //----------------------------------------------------------------------
    //
    //  Methods
    //
    //----------------------------------------------------------------------

    // Makes 1st letter of a string uppercase
    static upCase1st(string: string): string {
        return string.substr(0, 1).toUpperCase() + string.substr(1);
    }

    // Makes 1st letter of each sentence of a string uppercase
    static upCaseSentences(str: string) {
        return str.replace(/.+?[\.\?\!](\s|$)/g, function (txt) {
            return txt.charAt(0).toUpperCase() + txt.substr(1);
        });
    }
	
	// Return string number and suffix for a given num. Ex: 42 becomes '42nd'
	static suffixNum(num: number): string {
        return num + _NUM_SUFFIXES[num % 10];
    }

    // Puts "A" or "An" before string based on its first letter. //
    static AorAn(txt: string, UpCase?: boolean): string {
        var a: string = (GrammarUtil.VOWEL_ARRAY.indexOf(txt.toLowerCase().charAt(0)) > -1) ? "an " : "a ";
        if (UpCase) a = GrammarUtil.upCase1st(a);
        return a + txt;
    }

    // Adds punctuation at end of string, if needed. //
    static puncCheck(txt: string, UpCase?: boolean): string {
        txt = GrammarUtil.stripWhite(txt);
        if (txt.length) {
            if (GrammarUtil.PUNCTUATION_ARRAY.indexOf(txt.charAt(txt.length - 1)) === -1) {
                txt += ".";
            }
        }
        if (UpCase) txt = GrammarUtil.upCaseSentences(txt);
        return txt;
    }

    // Strips extra whitespace and optionally converts newlines and returns to spaces
    static stripWhite(txt: string, stripReturns?: boolean, stripNewlines?: boolean, newLineAndReturnToHTML?: boolean): string {
        const replaceWith: string = newLineAndReturnToHTML ? "<br>" : " ";
        // convert returns to spaces
      	if (stripReturns) {
            txt = txt.replace(/\r/g, replaceWith);
      	}
      	// convert newlines to spaces
      	if (stripNewlines) {
            txt = txt.replace(/\n/g, replaceWith);
      	}
      	// compress spaces
        const stringArray: string[] = txt.split(" ");
        for (var i = 0; i < stringArray.length; i++) {
            if (stringArray[i].length === 0) {
                stringArray.splice(i, 1);
            }
        }
        txt = stringArray.join(" ").trim();
        return txt;
    }

}