How can I implement some validation of content in Part Number field to ensure validity with ATA Spec2000 standard?

I have the minimum rules in the following JS code. Is there a preferred way for data validation at input, before SAVE (which could be ran through an event) .. 

            //function to verify part number meets Spec 2000
            function testPN() {
                let inputText = document.getElementById("pnText").value;
                //maximum number of characters allowed in the part number
                let maxChars = 15;

                //remove any leading and/or trailing spaces from the inputted part number
                inputText = inputText.trim();

                //Alert user if the submit button was pressed with no part number entered
                if (inputText == "") {
                    alert("Please enter a part number to analyze.");
                } else {
                    //define variables
                    let errorFound = false;
                    let errorText =  ];

                    //Verify max length
                    if (inputText.length > maxChars) {
                        errorFound = true;
                        errorText.push("The maximum number of characters is " + maxChars + ". The part number entered has " + inputText.length + ".");
                    }

                    //Verify no spaces
                    if (inputText.indexOf(' ') != -1) {
                        errorFound = true;
                        errorText.push("No spaces are allowed in the part number per ATA Spec 2000.");
                    }

                    //Verify uppercase only
                    let lowerPatt = new RegExp(""a-z]");
                    if (lowerPatt.test(inputText)) {
                        errorFound = true;
                        errorText.push("No lowercase letters are allowed per ATA Spec 2000.");
                    }

                    //Verify no use of the letter "O"
                    if (inputText.indexOf('O') != -1 || inputText.indexOf('o') != -1) {
                        errorFound = true;
                        errorText.push("The letter \"O\" is not allowed per ATA Spec 2000.");
                    }

                    //Verify does not start or end with "-"
                    let startingDash = new RegExp("^-");
                    let endingDash = new RegExp("-$");

                    if (startingDash.test(inputText) || endingDash.test(inputText)) {
                        errorFound = true;
                        errorText.push("The part number cannot start or end with a \"-\" per ATA Spec 2000.");
                    }

                    //Verify only use "-" beteen numeric characters
                    let numHyphen = new RegExp(""^0-9]-");
                    let hyphenNum = new RegExp("--^0-9]");

                    if (numHyphen.test(inputText) || hyphenNum.test(inputText)) {
                        errorFound = true;
                        errorText.push("Only numeric characters are allowed next to a hyphen per ATA Spec 2000.");
                    }

                    //verify no special characters used
                    //NOTE: lowercase letters, periods, and spaces are included since they are being checked elsewhere.
                    //      This prevents duplicate feedback entries.
                    let nonSpecial = new RegExp(""^0-9a-zA-Z-. ]");

                    if (nonSpecial.test(inputText)) {
                        errorFound = true;
                        errorText.push("No special characters (e.g. /, \\, *, &, #, etc.) are allowed per ATA Spec 2000.");
                    }


                    //Look for periods and warn if used
                    if (inputText.indexOf('.') !== -1) {
                        errorText.push("Note: The use of periods in the part number is allowed, but not recommended.");
                    }

                    //Compile feedback to user
                    let errorMessage = "";

                    if (errorFound) {
                        errorMessage = "<p style='color: red;'>The part number is not compliant with ATA Spec 2000.</p><p>";
                        for (let i = 0; i < errorText.length; i++) {
                            errorMessage += (i + 1) + ". " + errorTextti] + "<br>";
                        }
                        errorMessage += "</p>";

                    } else {
                        errorMessage = "<p>The part number is compliant with ATA Spec 2000.</p><p>";
                        for (let i = 0; i < errorText.length; i++) {
                            errorMessage += (i + 1) + ". " + errorTextti] + "<br>";
                        }
                        errorMessage += "</p>";
                    }

                    document.getElementById("feedback").innerHTML = errorMessage;

                }
            }