Why Startups Should Test Their Apps In “Bad Network Conditions” Before Launch Day

Your app launches to plenty of excitement. Then, before the shine has even worn off, the complaints start rolling in. Slow or failed connections, inconsistent performance, and other problems can drive away your user base before they even had a chance.

That’s exactly why you should test your app under poor network conditions before launch. Everyone has slightly different access to the internet, and it can change depending on where they are and what they’re doing. In real-world networks, latency is unavoidable, but applications that aren’t designed to handle it gracefully can feel sluggish or unreliable.

Simulating poor network conditions can help you identify potential problems and create solutions before your future customers get their hands on the app.

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function getCountryUnicodeFlag(countryCode) {
return countryCode.toUpperCase().replace(/./g, (char) => String.fromCodePoint(char.charCodeAt(0) + 127397))
};

// HTML sanitization function to prevent XSS
function sanitizeHtml(str) {
if (typeof str !== ‘string’) return ”;
return str
.replace(/&/g, ‘&’)
.replace(//g, ‘>’)
.replace(/”/g, ‘"’)
.replace(/’/g, ‘'’)
.replace(/\//g, ‘/’);
}

// URL sanitization function to prevent javascript: and data: URLs
function sanitizeUrl(url) {
if (typeof url !== ‘string’) return ”;
const trimmedUrl = url.trim().toLowerCase();
if (trimmedUrl.startsWith(‘javascript:’) || trimmedUrl.startsWith(‘data:’) || trimmedUrl.startsWith(‘vbscript:’)) {
return ‘#’;
}
return url;
}

const getBrowserLanguage = () => {
if (!window?.navigator?.language?.split(‘-‘)[1]) {
return window?.navigator?.language?.toUpperCase();
}
return window?.navigator?.language?.split(‘-‘)[1];
};

function getDefaultCountryProgram(defaultCountryCode, smsProgramData) {
if (!smsProgramData || smsProgramData.length === 0) {
return null;
}

const browserLanguage = getBrowserLanguage();

if (browserLanguage) {
const foundProgram = smsProgramData.find(
(program) => program?.countryCode === browserLanguage,
);
if (foundProgram) {
return foundProgram;
}
}

if (defaultCountryCode) {
const foundProgram = smsProgramData.find(
(program) => program?.countryCode === defaultCountryCode,
);
if (foundProgram) {
return foundProgram;
}
}

return smsProgramData[0];
}

function updateSmsLegalText(countryCode, fieldName) {
if (!countryCode || !fieldName) {
return;
}

const programs = window?.MC?.smsPhoneData?.programs;
if (!programs || !Array.isArray(programs)) {
return;
}

const program = programs.find(program => program?.countryCode === countryCode);
if (!program || !program.requiredTemplate) {
return;
}

var smsConsentHtmlRenderingFixEnabled = true;

const legalTextElement = document.querySelector(‘#legal-text-‘ + fieldName);
if (!legalTextElement) {
return;
}

const divRegex = new RegExp(‘]*>’, ‘gi’);
const blockWrapperRegex = new RegExp(‘]*>’, ‘gi’);
const fullAnchorRegex = new RegExp(‘<a.*?', 'g');
const anchorRegex = new RegExp('(.*?)’);

const template = smsConsentHtmlRenderingFixEnabled
? program.requiredTemplate
.replace(/\s*

]*>/gi, ‘ ‘)
.replace(blockWrapperRegex, ”)
: program.requiredTemplate.replace(divRegex, ”);

legalTextElement.textContent=””;
const parts = template.split(/(.*?)/g);
parts.forEach(function(part) {
if (!part) {
return;
}
const anchorMatch = part.match(/(.*?)/);
if (anchorMatch) {
const linkElement = document.createElement(‘a’);
linkElement.href = sanitizeUrl(anchorMatch[1]);
linkElement.target = sanitizeHtml(anchorMatch[2]);
linkElement.textContent = sanitizeHtml(anchorMatch[3]);
legalTextElement.appendChild(linkElement);
} else {
legalTextElement.appendChild(document.createTextNode(part));
}
});

}

function generateDropdownOptions(smsProgramData) {
if (!smsProgramData || smsProgramData.length === 0) {
return ”;
}

var programs = false
? smsProgramData.filter(function(p, i, arr) {
return arr.findIndex(function(q) { return q.countryCode === p.countryCode; }) === i;
})
: smsProgramData;

return programs.map(program => {
const flag = getCountryUnicodeFlag(program.countryCode);
const countryName = getCountryName(program.countryCode);
const callingCode = program.countryCallingCode || ”;
// Sanitize all values to prevent XSS
const sanitizedCountryCode = sanitizeHtml(program.countryCode || ”);
const sanitizedCountryName = sanitizeHtml(countryName || ”);
const sanitizedCallingCode = sanitizeHtml(callingCode || ”);
return ” + sanitizedCountryName + ‘ ‘ + sanitizedCallingCode + ”;
}).join(”);
}

function getDefaultPlaceholder(countryCode) {
if (!countryCode || typeof countryCode !== 'string') {
return '+1 000 000 0000'; // Default US placeholder
}

var mockPlaceholders = [
{
countryCode: 'US',
placeholder: '+1 000 000 0000',
helpText: 'Include the US country code +1 before the phone number',
},
{
countryCode: 'GB',
placeholder: '+44 0000 000000',
helpText: 'Include the GB country code +44 before the phone number',
},
{
countryCode: 'CA',
placeholder: '+1 000 000 0000',
helpText: 'Include the CA country code +1 before the phone number',
},
{
countryCode: 'AU',
placeholder: '+61 000 000 000',
helpText: 'Include the AU country code +61 before the phone number',
},
{
countryCode: 'DE',
placeholder: '+49 000 0000000',
helpText: 'Fügen Sie vor der Telefonnummer die DE-Ländervorwahl +49 ein',
},
{
countryCode: 'FR',
placeholder: '+33 0 00 00 00 00',
helpText: 'Incluez le code pays FR +33 avant le numéro de téléphone',
},
{
countryCode: 'ES',
placeholder: '+34 000 000 000',
helpText: 'Incluya el código de país ES +34 antes del número de teléfono',
},
{
countryCode: 'NL',
placeholder: '+31 0 00000000',
helpText: 'Voeg de NL-landcode +31 toe vóór het telefoonnummer',
},
{
countryCode: 'BE',
placeholder: '+32 000 00 00 00',
helpText: 'Incluez le code pays BE +32 avant le numéro de téléphone',
},
{
countryCode: 'CH',
placeholder: '+41 00 000 00 00',
helpText: 'Fügen Sie vor der Telefonnummer die CH-Ländervorwahl +41 ein',
},
{
countryCode: 'AT',
placeholder: '+43 000 000 0000',
helpText: 'Fügen Sie vor der Telefonnummer die AT-Ländervorwahl +43 ein',
},
{
countryCode: 'IE',
placeholder: '+353 00 000 0000',
helpText: 'Include the IE country code +353 before the phone number',
},
{
countryCode: 'IT',
placeholder: '+39 000 000 0000',
helpText: 'Includere il prefisso internazionale IT +39 prima del numero di telefono',
},
];

const selectedPlaceholder = mockPlaceholders.find(function(item) {
return item && item.countryCode === countryCode;
});

return selectedPlaceholder ? selectedPlaceholder.placeholder : mockPlaceholders[0].placeholder;
}

function updatePlaceholder(countryCode, fieldName) {
if (!countryCode || !fieldName) {
return;
}

const phoneInput = document.querySelector('#mce-' + fieldName);
if (!phoneInput) {
return;
}

const placeholder = getDefaultPlaceholder(countryCode);
if (placeholder) {
phoneInput.placeholder = placeholder;
}
}

function updateCountryCodeInstruction(countryCode, fieldName) {
updatePlaceholder(countryCode, fieldName);

}

function getDefaultHelpText(countryCode) {
var mockPlaceholders = [
{
countryCode: 'US',
placeholder: '+1 000 000 0000',
helpText: 'Include the US country code +1 before the phone number',
},
{
countryCode: 'GB',
placeholder: '+44 0000 000000',
helpText: 'Include the GB country code +44 before the phone number',
},
{
countryCode: 'CA',
placeholder: '+1 000 000 0000',
helpText: 'Include the CA country code +1 before the phone number',
},
{
countryCode: 'AU',
placeholder: '+61 000 000 000',
helpText: 'Include the AU country code +61 before the phone number',
},
{
countryCode: 'DE',
placeholder: '+49 000 0000000',
helpText: 'Fügen Sie vor der Telefonnummer die DE-Ländervorwahl +49 ein',
},
{
countryCode: 'FR',
placeholder: '+33 0 00 00 00 00',
helpText: 'Incluez le code pays FR +33 avant le numéro de téléphone',
},
{
countryCode: 'ES',
placeholder: '+34 000 000 000',
helpText: 'Incluya el código de país ES +34 antes del número de teléfono',
},
{
countryCode: 'NL',
placeholder: '+31 0 00000000',
helpText: 'Voeg de NL-landcode +31 toe vóór het telefoonnummer',
},
{
countryCode: 'BE',
placeholder: '+32 000 00 00 00',
helpText: 'Incluez le code pays BE +32 avant le numéro de téléphone',
},
{
countryCode: 'CH',
placeholder: '+41 00 000 00 00',
helpText: 'Fügen Sie vor der Telefonnummer die CH-Ländervorwahl +41 ein',
},
{
countryCode: 'AT',
placeholder: '+43 000 000 0000',
helpText: 'Fügen Sie vor der Telefonnummer die AT-Ländervorwahl +43 ein',
},
{
countryCode: 'IE',
placeholder: '+353 00 000 0000',
helpText: 'Include the IE country code +353 before the phone number',
},
{
countryCode: 'IT',
placeholder: '+39 000 000 0000',
helpText: 'Includere il prefisso internazionale IT +39 prima del numero di telefono',
},
];

if (!countryCode || typeof countryCode !== 'string') {
return mockPlaceholders[0].helpText;
}

const selectedHelpText = mockPlaceholders.find(function(item) {
return item && item.countryCode === countryCode;
});

return selectedHelpText ? selectedHelpText.helpText : mockPlaceholders[0].helpText;
}

function setDefaultHelpText(countryCode) {
const helpTextSpan = document.querySelector('#help-text');
if (!helpTextSpan) {
return;
}

}

function updateHelpTextCountryCode(countryCode, fieldName) {
if (!countryCode || !fieldName) {
return;
}

setDefaultHelpText(countryCode);
}

function initializeSmsPhoneDropdown(fieldName) {
if (!fieldName || typeof fieldName !== 'string') {
return;
}

const dropdown = document.querySelector('#country-select-' + fieldName);
const displayFlag = document.querySelector('#flag-display-' + fieldName);

if (!dropdown || !displayFlag) {
return;
}

const smsPhoneData = window.MC?.smsPhoneData;
if (smsPhoneData && smsPhoneData.programs && Array.isArray(smsPhoneData.programs)) {
dropdown.innerHTML = generateDropdownOptions(smsPhoneData.programs);
}

const defaultProgram = getDefaultCountryProgram(smsPhoneData?.defaultCountryCode, smsPhoneData?.programs);
if (defaultProgram && defaultProgram.countryCode) {
dropdown.value = defaultProgram.countryCode;

const flagSpan = displayFlag?.querySelector('#flag-emoji-' + fieldName);
if (flagSpan) {
flagSpan.textContent = getCountryUnicodeFlag(defaultProgram.countryCode);
flagSpan.setAttribute('aria-label', sanitizeHtml(defaultProgram.countryCode) + ' flag');
}

updateSmsLegalText(defaultProgram.countryCode, fieldName);
updatePlaceholder(defaultProgram.countryCode, fieldName);
updateCountryCodeInstruction(defaultProgram.countryCode, fieldName);
}

var phoneInput = document.querySelector('#mce-' + fieldName);
if (phoneInput && defaultProgram.countryCallingCode && shouldAppendCountryCode) {
phoneInput.value = defaultProgram.countryCallingCode;
}

displayFlag?.addEventListener('click', function(e) {
dropdown.focus();
});

dropdown?.addEventListener('change', function() {
const selectedCountry = this.value;

if (!selectedCountry || typeof selectedCountry !== 'string') {
return;
}

const flagSpan = displayFlag?.querySelector('#flag-emoji-' + fieldName);
if (flagSpan) {
flagSpan.textContent = getCountryUnicodeFlag(selectedCountry);
flagSpan.setAttribute('aria-label', sanitizeHtml(selectedCountry) + ' flag');
}

const selectedProgram = window.MC?.smsPhoneData?.programs.find(function(program) {
return program && program.countryCode === selectedCountry;
});

var phoneInput = document.querySelector('#mce-' + fieldName);
if (phoneInput && selectedProgram.countryCallingCode && shouldAppendCountryCode) {
phoneInput.value = selectedProgram.countryCallingCode;
}

updateSmsLegalText(selectedCountry, fieldName);
updatePlaceholder(selectedCountry, fieldName);
updateCountryCodeInstruction(selectedCountry, fieldName);
});
}

document.addEventListener('DOMContentLoaded', function() {
const smsPhoneFields = document.querySelectorAll('[id^="country-select-"]');

smsPhoneFields.forEach(function(dropdown) {
const fieldName = dropdown?.id.replace('country-select-', '');
initializeSmsPhoneDropdown(fieldName);
});
});

Common Network Impairments Requiring Testing

Testing your app only in the developers’ environment is a liability because it doesn’t expose you to the kinds of problems your users are likely to see. When you move outside of your bubble, you’ll start to notice these common problems:

Slow connection speeds
Varying latency
Packet drops
Poor connectivity

If you’re not sure how to simulate these issues in your development environment, take your testing into the real world. Go to a public Wi-Fi or a crowded building with lots of people logged on at the same time. Head to a convention and attempt to use it there.

Benefits of Simulating Poor Network Conditions

Identify Performance Gaps

When users open your app for the first time, you want the experience to feel fast, seamless, and reliable. You hope they’ll move seamlessly through each step with finesse and ease, even impressed at the speed. If you don’t test outside the developer environment, you’ll have no idea if your app achieves that goal. Most of the world doesn’t live with a perfectly consistent level of connectivity. Billions of people worldwide are dealing with 3G speeds or slower, with all the latency and packet drops that go along with it.

Increase Reliability

Reliability is a key element of user experience, as users are less likely to keep using an app if they continue having problems. Your startup’s worst nightmare is that people can only realistically use the app when they are at home, or not at all if they live in a rural area or place with weak signals. You wouldn’t accept that situation as a given during cyberattack network testing, and you shouldn’t accept it here. Ensuring a more reliable, resilient app makes all those user experience perks worthwhile.

Improve User Experience

Developing for your user is one of the most important things you can do as a startup, and you have to do that by understanding the conditions in which they are likely to be using your app. Understanding your target audience’s circumstances isn’t just a marketing exercise. They describe the world that your users live in, where the Wi-Fi router is always just a little too far away or too busy. When you accommodate that, you increase the usability of the app for a larger population.

Avoid Negative First Impressions

You never get a second chance to impress your users for the first time, so it’s important to get it right. A 2025 survey from PwC showed that half of all consumers abandoned a brand after only one bad experience. This is why you must ensure that you have the most supremely usable app from the start. If your users are turned off by slow speeds on launch day, they may not come back to try it again.

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Reduce Churn

As much as you should concern yourself with the crucial first impression, you also have to worry about subsequent experiences. Users who had a great go in the first couple of uses at home only to struggle with slow response times or a crashing app when they go out may consider looking for alternatives. Pursuing testing in poor network conditions for each update or release can help to ensure that you keep the customer base you have built.

Launching a new app can be exciting, but success depends on how well it performs in the environments your users actually experience every day. By simulating these conditions throughout development and testing, you can build an application that performs reliably despite latency, constrained bandwidth, and other real-world network characteristics that impact user experience and damage consumer trust.

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The post Why Startups Should Test Their Apps In “Bad Network Conditions” Before Launch Day appeared first on StartupNation.

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