---
original_url: "https://jace.pro/blog/client-script-validating-emails/"
format: markdown
ai_optimized: true
---

Client Script - Validating emails- # Client Script - Validating emails

September 26, 2017 [client-scripts ](/tags/client-scripts/)[servicenow](/tags/servicenow/)

  Enable AI AnimationI suggest you don’t use it as you can’t ensure the data.

I found two real ways to verify the data meets the needs you have.

Client script to do entire validation
- Client script to ask server if data is valid

This will use all client-side validation.

`// Name: Email Validator
// Type: onSubmit
// UI Type: All
function onSubmit() {
    var field = 'email';
    g_form.hideFieldMsg(field, true);
    return isEmailValid(field, g_form.getValue(field));
}

function isEmailValid(field, value) {
    var problemMsg = isEmailValidWithReason(value);
    if (problemMsg !== "") {
        //jslog("isEmailValid: " + problemMsg);
        g_form.showFieldMsg(field, problemMsg, 'error', true);
        return false;
    }
    return true;
}

function isEmailValidWithReason(value) {
    var localPartChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!#$%*/?|^{}`~&'+-=_.",
        domainChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.";
    if (value.indexOf("@") == -1) {
        return "missing @ sign";
    }
    var s = value.split("@");
    if (s.length != 2) {
        return "one at signs allowed";
    }
    if (!containsOnlyChars(localPartChars, s[0])) {
        return "invalid character before the at sign";
    }
    if (s[0].length < 1) {
        return "at least one character must be before the at sign";
    }
    if (s[0].substr(0, 1) == ".") {
        return "period cannot be the first character";
    }
    if (s[0].substr(s[0].length - 1, 1) == ".") {
        return "period cannot be the last character before the at sign";
    }
    if (!containsOnlyChars(domainChars, s[1])) {
        return "invalid character after the at sign";
    }
    var periodIndex = s[1].indexOf(".");
    if (periodIndex == -1) {
        return "missing period after the at sign";
    }
    if (periodIndex === 0) {
        return "period cannot be the first character after the at sign";
    }
    var periods = s[1].split(".");
    var lastPeriod = periods[periods.length - 1];
    if (lastPeriod.length < 1) {
        return "must be at least 1 character after the last period";
    }
    if (!isAlphaNum(s[1].substr(0, 1))) {
        return "the first character after the at sign must be alphanumeric";
    }
    if (!isAlphaNum(s[1].substr(s[1].length - 1, 1))) {
        return "the last character must be alphanumeric";
    }
    return "";
}

function isAlpha(thchar) {
    return (thchar >= 'a' && thchar <= 'z\uffff') || (thchar >= 'A' && thchar <= 'Z\uffff') || thchar == '_';
}

function isAlphaNum(thchar) {
    return isAlpha(thchar) || isDigit(thchar);
}

function isDigit(thchar) {
    return (thchar >= '0' && thchar <= '9');
}

function containsOnlyChars(validChars, sText) {
    if (!sText)
        return true;
    for (var i = 0; i < sText.length; i++) {
        var c = sText.charAt(i);
        if (validChars.indexOf(c) == -1)
            return false;
    }
    return true;
}`
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[View this page on GitHub](https://github.com/jacebenson/jace.pro/tree/main/./src/posts/2017/2017-09-25-validating-emails.md).

[Client Script - Validating emails](https://jace.pro/blog/client-script-validating-emails/) [Jace Benson](https://jace.pro) ![Jace Benson](https://jace.pro/icon-512x512.png)

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*This content is from Jace Benson's ServiceNow and tech blog at jace.pro*
*Original post: https://jace.pro/blog/client-script-validating-emails/*