javascript 48 lines · 8 steps

Building a live password strength meter

A debounced input handler scores passwords with zxcvbn and paints a color-coded strength bar in real time.

Explained by highlit
Intermediate debounce closures dom-events accessibility event-driven
1const zxcvbn = require('zxcvbn');
2 
3const STRENGTH_LABELS = ['Very weak', 'Weak', 'Fair', 'Strong', 'Very strong'];
4const STRENGTH_COLORS = ['#d64545', '#e0803c', '#d9c94c', '#5aa84f', '#2f8f3a'];
5 
6function initPasswordMeter(input, meter) {
7 const bar = meter.querySelector('.meter-bar');
8 const label = meter.querySelector('.meter-label');
9 const feedback = meter.querySelector('.meter-feedback');
10 const toggle = meter.querySelector('.toggle-visibility');
11 
12 const render = debounce((value) => {
13 if (!value) {
14 bar.style.width = '0%';
15 label.textContent = '';
16 feedback.textContent = '';
17 return;
18 }
19 
20 const { score, feedback: hints } = zxcvbn(value);
21 bar.style.width = `${(score + 1) * 20}%`;
22 bar.style.backgroundColor = STRENGTH_COLORS[score];
23 label.textContent = STRENGTH_LABELS[score];
24 feedback.textContent = hints.warning || hints.suggestions[0] || '';
25 }, 150);
26 
27 input.addEventListener('input', (e) => render(e.target.value));
28 
29 toggle.addEventListener('click', () => {
30 const masked = input.type === 'password';
31 input.type = masked ? 'text' : 'password';
32 toggle.setAttribute('aria-pressed', String(masked));
33 toggle.textContent = masked ? 'Hide' : 'Show';
34 });
35}
36 
37function debounce(fn, wait) {
38 let timer;
39 return (...args) => {
40 clearTimeout(timer);
41 timer = setTimeout(() => fn(...args), wait);
42 };
43}
44 
45document.querySelectorAll('[data-password-meter]').forEach((meter) => {
46 const input = document.getElementById(meter.dataset.passwordMeter);
47 if (input) initPasswordMeter(input, meter);
48});
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Debouncing an expensive scoring call keeps live feedback smooth while the user is still typing.
  2. 2Mapping a numeric score to parallel label and color arrays turns raw output into clear visual UI.
  3. 3Wiring behavior from a data attribute lets one initializer serve every meter on the page.

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