Real Zepto Interview Experience

// toast-context.jsx
import { createContext, useContext, useReducer, useCallback, useRef } from 'react';

const ToastContext = createContext(null);

const TOAST_LIMIT = 3;
const DEFAULT_DURATION = 3000;

function toastReducer(state, action) {
  switch (action.type) {
    case 'ADD':
      return {
        ...state,
        toasts: [...state.toasts, action.payload],
        queue: state.toasts.length >= TOAST_LIMIT
          ? [...state.queue, action.payload]
          : state.queue,
      };
    case 'REMOVE':
      const remaining = state.toasts.filter(t => t.id !== action.id);
      // Pull from queue if available
      if (state.queue.length > 0 && remaining.length < TOAST_LIMIT) {
        const [next, ...restQueue] = state.queue;
        return { toasts: [...remaining, next], queue: restQueue };
      }
      return { ...state, toasts: remaining };
    default:
      return state;
  }
}

export function ToastProvider({ children, position = 'top-right' }) {
  const [state, dispatch] = useReducer(toastReducer, { toasts: [], queue: [] });
  const toastId = useRef(0);

  const addToast = useCallback(({ message, variant = 'info', duration = DEFAULT_DURATION }) => {
    const id = ++toastId.current;
    dispatch({ type: 'ADD', payload: { id, message, variant, duration } });

    if (duration > 0) {
      setTimeout(() => {
        dispatch({ type: 'REMOVE', id });
      }, duration);
    }

    return id;
  }, []);

  const removeToast = useCallback((id) => {
    dispatch({ type: 'REMOVE', id });
  }, []);

  return (
    <ToastContext.Provider value={{ addToast, removeToast }}>
      {children}
      <ToastContainer toasts={state.toasts} position={position} onDismiss={removeToast} />
    </ToastContext.Provider>
  );
}

export const useToast = () => useContext(ToastContext);

// Solution: Move toast state OUTSIDE React using a store pattern
// Only the ToastContainer subscribes to changes

let listeners = [];
let toasts = [];

const toastStore = {
  getState: () => toasts,
  subscribe: (listener) => {
    listeners.push(listener);
    return () => { listeners = listeners.filter(l => l !== listener); };
  },
  addToast: (toast) => {
    toasts = [...toasts, { ...toast, id: Date.now() }];
    listeners.forEach(l => l());
  },
  removeToast: (id) => {
    toasts = toasts.filter(t => t.id !== id);
    listeners.forEach(l => l());
  }
};

// Only ToastContainer subscribes — rest of app never re-renders
function ToastContainer() {
  const [state, setState] = useState(toastStore.getState());

  useEffect(() => {
    return toastStore.subscribe(() => setState(toastStore.getState()));
  }, []);

  return (
    <div className="toast-container">
      {state.slice(0, TOAST_LIMIT).map(toast => (
        <Toast key={toast.id} {...toast} onDismiss={() => toastStore.removeToast(toast.id)} />
      ))}
    </div>
  );
}

// Any component can trigger toasts without prop drilling or context re-renders
// import { toastStore } from './toast-store';
// toastStore.addToast({ message: 'Saved!', variant: 'success' });

import { useRef, useImperativeHandle, forwardRef } from 'react';

// Expose dismiss method via ref
const ToastManager = forwardRef((props, ref) => {
  const [toasts, setToasts] = useState([]);

  useImperativeHandle(ref, () => ({
    dismiss: (id) => {
      setToasts(prev => prev.filter(t => t.id !== id));
    },
    dismissAll: () => {
      setToasts([]);
    },
    add: (toast) => {
      const id = Date.now();
      setToasts(prev => [...prev, { ...toast, id }]);
      return id; // Return id for programmatic dismiss
    }
  }));

  return (
    <div className="toast-container">
      {toasts.map(t => <Toast key={t.id} {...t} />)}
    </div>
  );
});

// Usage in parent
function App() {
  const toastRef = useRef();

  const handleSave = async () => {
    const loadingId = toastRef.current.add({
      message: 'Saving...',
      variant: 'info',
      duration: 0 // persistent
    });

    await saveData();

    // Programmatically dismiss loading toast
    toastRef.current.dismiss(loadingId);
    toastRef.current.add({ message: 'Saved!', variant: 'success' });
  };

  return (
    <>
      <button onClick={handleSave}>Save</button>
      <ToastManager ref={toastRef} />
    </>
  );
}

import { useState, useRef, useCallback } from 'react';

function OTPInput({ length = 6, onComplete }) {
  const [otp, setOtp] = useState(new Array(length).fill(''));
  const inputRefs = useRef([]);

  const handleChange = useCallback((e, index) => {
    const value = e.target.value;
    if (!/^\d*$/.test(value)) return; // Only digits

    const newOtp = [...otp];
    // Take only last character (handles overwrite)
    newOtp[index] = value.slice(-1);
    setOtp(newOtp);

    // Auto-focus next input
    if (value && index < length - 1) {
      inputRefs.current[index + 1].focus();
    }

    // Check if complete
    const otpString = newOtp.join('');
    if (otpString.length === length && onComplete) {
      onComplete(otpString);
    }
  }, [otp, length, onComplete]);

  const handleKeyDown = useCallback((e, index) => {
    if (e.key === 'Backspace') {
      if (!otp[index] && index > 0) {
        // If current box empty, move to previous
        inputRefs.current[index - 1].focus();
        const newOtp = [...otp];
        newOtp[index - 1] = '';
        setOtp(newOtp);
      }
    }
  }, [otp]);

  const handlePaste = useCallback((e) => {
    e.preventDefault();
    const pastedData = e.clipboardData.getData('text').slice(0, length);
    if (!/^\d+$/.test(pastedData)) return;

    const newOtp = [...otp];
    pastedData.split('').forEach((digit, i) => {
      newOtp[i] = digit;
    });
    setOtp(newOtp);

    // Focus last filled or next empty
    const focusIndex = Math.min(pastedData.length, length - 1);
    inputRefs.current[focusIndex].focus();

    if (pastedData.length === length && onComplete) {
      onComplete(pastedData);
    }
  }, [otp, length, onComplete]);

  return (
    <div style={{ display: 'flex', gap: '8px' }}>
      {otp.map((digit, index) => (
        <input
          key={index}
          ref={(el) => (inputRefs.current[index] = el)}
          type="text"
          inputMode="numeric"
          maxLength={1}
          value={digit}
          onChange={(e) => handleChange(e, index)}
          onKeyDown={(e) => handleKeyDown(e, index)}
          onPaste={handlePaste}
          style={{
            width: '48px', height: '48px',
            textAlign: 'center', fontSize: '1.5rem',
            border: '2px solid #ddd', borderRadius: '8px'
          }}
        />
      ))}
    </div>
  );
}

import { useState, useEffect, useRef, useCallback } from 'react';

function useDebounce(value, delay) {
  const [debounced, setDebounced] = useState(value);
  useEffect(() => {
    const timer = setTimeout(() => setDebounced(value), delay);
    return () => clearTimeout(timer);
  }, [value, delay]);
  return debounced;
}

function TypeAheadSearch({ fetchSuggestions, onSelect }) {
  const [query, setQuery] = useState('');
  const [results, setResults] = useState([]);
  const [loading, setLoading] = useState(false);
  const [activeIndex, setActiveIndex] = useState(-1);
  const [isOpen, setIsOpen] = useState(false);
  const abortRef = useRef(null);
  const containerRef = useRef(null);

  const debouncedQuery = useDebounce(query, 300);

  // Fetch results
  useEffect(() => {
    if (!debouncedQuery.trim()) {
      setResults([]);
      setIsOpen(false);
      return;
    }

    // Cancel previous request
    if (abortRef.current) abortRef.current.abort();
    abortRef.current = new AbortController();

    setLoading(true);
    fetchSuggestions(debouncedQuery, abortRef.current.signal)
      .then((data) => {
        setResults(data);
        setIsOpen(true);
        setActiveIndex(-1);
      })
      .catch((err) => {
        if (err.name !== 'AbortError') setResults([]);
      })
      .finally(() => setLoading(false));
  }, [debouncedQuery, fetchSuggestions]);

  // Click outside to close
  useEffect(() => {
    const handleClick = (e) => {
      if (containerRef.current && !containerRef.current.contains(e.target)) {
        setIsOpen(false);
      }
    };
    document.addEventListener('mousedown', handleClick);
    return () => document.removeEventListener('mousedown', handleClick);
  }, []);

  const handleKeyDown = useCallback((e) => {
    if (!isOpen) return;

    switch (e.key) {
      case 'ArrowDown':
        e.preventDefault();
        setActiveIndex(prev => Math.min(prev + 1, results.length - 1));
        break;
      case 'ArrowUp':
        e.preventDefault();
        setActiveIndex(prev => Math.max(prev - 1, 0));
        break;
      case 'Enter':
        if (activeIndex >= 0) {
          onSelect(results[activeIndex]);
          setIsOpen(false);
          setQuery(results[activeIndex].label);
        }
        break;
      case 'Escape':
        setIsOpen(false);
        break;
    }
  }, [isOpen, results, activeIndex, onSelect]);

  return (
    <div ref={containerRef} style={{ position: 'relative' }}>
      <input
        value={query}
        onChange={(e) => setQuery(e.target.value)}
        onKeyDown={handleKeyDown}
        onFocus={() => results.length > 0 && setIsOpen(true)}
        placeholder="Search..."
      />
      {loading && <span className="spinner" />}
      {isOpen && results.length > 0 && (
        <ul className="dropdown">
          {results.map((item, i) => (
            <li
              key={item.id}
              className={i === activeIndex ? 'active' : ''}
              onClick={() => { onSelect(item); setIsOpen(false); setQuery(item.label); }}
              onMouseEnter={() => setActiveIndex(i)}
            >
              {item.label}
            </li>
          ))}
        </ul>
      )}
    </div>
  );
}