Code Block

React Native

Streaming code with fixed line numbers and wrap.

Install

Source on GitHub

It works in Expo and in bare React Native. New to beUI Native? Set up your app first.

$ bunx beui-native add

Copies the component and the shared files it needs into src/, adds the theme tokens if they're missing, and installs its libraries. Files you've changed are kept.

Keep the folder layout, since the component imports the shared files by relative path.

1Install the libraries

npx expo install prism-react-renderer react-native-reanimated react-native-svg react-native-worklets
npm install uniwind tailwindcss

2Add the theme tokens

Once per app. Import it from the CSS file Uniwind reads, after Tailwind and Uniwind, and change the values to match your brand.

CSSsrc/styles/theme.css

/* Matches the default beUI palette in ui-components/lib/themes.ts.
   Native surface maps to card; muted maps to muted-foreground. */
@layer theme {
  :root {
    @variant light {
      --color-background: oklch(99% 0 0);
      --color-surface: oklch(97% 0 0);
      --color-foreground: oklch(15% 0 0);
      --color-muted: oklch(50% 0 0);
      --color-border: oklch(15% 0 0 / 0.06);
      --color-border-strong: oklch(15% 0 0 / 0.16);
      --color-primary: #0285f7;
      --color-on-primary: #ffffff;
      --color-destructive: #dc2626;
      --color-success: #059669;
      --color-warning: #d97706;
    }
  }

  :root {
    @variant dark {
      --color-background: #151515;
      --color-surface: #1c1c1c;
      --color-foreground: oklch(96% 0 0);
      --color-muted: oklch(62% 0 0);
      --color-border: rgb(255 255 255 / 0.05);
      --color-border-strong: rgb(255 255 255 / 0.14);
      --color-primary: #0285f7;
      --color-on-primary: #ffffff;
      --color-destructive: #f87171;
      --color-success: #34d399;
      --color-warning: #fbbf24;
    }
  }

  /* Tailwind's default monospace stack isn't a font React Native can load. */
  :root {
    @variant ios {
      --font-mono: Menlo;
    }
  }

  :root {
    @variant android {
      --font-mono: monospace;
    }
  }
}

3Copy the shared files

TSsrc/hooks/use-reduced-motion.ts

import { useEffect, useState } from "react";
import { AccessibilityInfo } from "react-native";
import { useReducedMotion } from "react-native-reanimated";

/** Reanimated supplies a synchronous initial value; native events keep it current. */
export function useReducedMotionPreference() {
  const initialValue = useReducedMotion();
  const [reducedMotion, setReducedMotion] = useState(initialValue);

  useEffect(() => {
    let active = true;
    let receivedEvent = false;
    const subscription = AccessibilityInfo.addEventListener(
      "reduceMotionChanged",
      (value) => {
        receivedEvent = true;
        setReducedMotion(value);
      },
    );
    void AccessibilityInfo.isReduceMotionEnabled().then((value) => {
      if (active && !receivedEvent) setReducedMotion(value);
    });
    return () => {
      active = false;
      subscription.remove();
    };
  }, []);

  return reducedMotion;
}

TSXsrc/primitives/agent-icons.tsx

import type { ReactNode } from "react";
import type { ColorValue } from "react-native";
import Svg, { Circle, Path, Rect } from "react-native-svg";

type GlyphProps = { size?: number; color?: ColorValue; strokeWidth?: number };

function Glyph({
  size = 16,
  color = "currentColor",
  strokeWidth = 2,
  children,
}: GlyphProps & { children: ReactNode }) {
  return (
    <Svg
      width={size}
      height={size}
      viewBox="0 0 24 24"
      fill="none"
      stroke={color}
      strokeWidth={strokeWidth}
      strokeLinecap="round"
      strokeLinejoin="round"
    >
      {children}
    </Svg>
  );
}

// Simple 24-unit stroke glyphs shared by the agent components.

export function ChevronDownGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M6 9l6 6 6-6" />
    </Glyph>
  );
}

export function ArrowUpGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M12 19V5M5.5 11.5L12 5l6.5 6.5" />
    </Glyph>
  );
}

export function PlusGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M12 5v14M5 12h14" />
    </Glyph>
  );
}

export function StopGlyph({ size = 12, color }: GlyphProps) {
  return (
    <Svg width={size} height={size} viewBox="0 0 12 12">
      <Rect x={1} y={1} width={10} height={10} rx={2.5} fill={color} />
    </Svg>
  );
}

export function CheckGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M5 12.5l4.5 4.5L19 7" />
    </Glyph>
  );
}

export function CopyGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Rect x={8.5} y={8.5} width={12} height={12} rx={2.5} />
      <Path d="M15.5 5.5v-.5A2 2 0 0 0 13.5 3h-8.5A2 2 0 0 0 3 5v8.5a2 2 0 0 0 2 2h.5" />
    </Glyph>
  );
}

export function RetryGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M3.5 12a8.5 8.5 0 1 0 2.6-6.1L3.5 8.5" />
      <Path d="M3.5 3.5v5h5" />
    </Glyph>
  );
}

export function ThumbGlyph({
  down = false,
  ...props
}: GlyphProps & { down?: boolean }) {
  return (
    <Glyph {...props}>
      <Path
        d="M7.5 10.5v10M7.5 10.5L11 3.5a2.5 2.5 0 0 1 2.5 2.5v3.5h5a2 2 0 0 1 2 2.3l-1.2 7A2 2 0 0 1 17.3 20.5H4.5a1 1 0 0 1-1-1v-8a1 1 0 0 1 1-1z"
        transform={down ? "rotate(180 12 12)" : undefined}
      />
    </Glyph>
  );
}

export function SearchGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={11} cy={11} r={6.5} />
      <Path d="M16 16l4 4" />
    </Glyph>
  );
}

export function GlobeGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={12} cy={12} r={8.5} />
      <Path d="M3.5 12h17M12 3.5c2.4 2.5 3.5 5.3 3.5 8.5s-1.1 6-3.5 8.5c-2.4-2.5-3.5-5.3-3.5-8.5s1.1-6 3.5-8.5z" />
    </Glyph>
  );
}

export function FileGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M14 3.5H7.5a2 2 0 0 0-2 2v13a2 2 0 0 0 2 2h9a2 2 0 0 0 2-2V8z" />
      <Path d="M14 3.5V8h4.5M9 13h6M9 16.5h4" />
    </Glyph>
  );
}

export function PencilGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M4 20h4L19 9a2.1 2.1 0 0 0-4-4L4 16z" />
      <Path d="M13.5 6.5l4 4M14 20h6" />
    </Glyph>
  );
}

export function TerminalGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Rect x={3.5} y={4.5} width={17} height={15} rx={2.5} />
      <Path d="M7.5 10l2.5 2-2.5 2M12.5 15h4" />
    </Glyph>
  );
}

export function WrenchGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M14.5 6.5a4 4 0 0 0 5 5l-8.8 8.8a2.1 2.1 0 0 1-3-3l8.8-8.8a4 4 0 0 1-2-2z" />
    </Glyph>
  );
}

export function SparkleGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M12 4l1.8 4.6L18.5 10.5l-4.7 1.9L12 17l-1.8-4.6-4.7-1.9 4.7-1.9z" />
      <Path d="M18.5 16.5v3M17 18h3" />
    </Glyph>
  );
}

export function MessageGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M20 14.5a2 2 0 0 1-2 2H8.5L4 20V6a2 2 0 0 1 2-2h12a2 2 0 0 1 2 2z" />
    </Glyph>
  );
}

export function ImageGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Rect x={3.5} y={4.5} width={17} height={15} rx={2.5} />
      <Circle cx={9} cy={10} r={1.5} />
      <Path d="M20.5 15.5l-4.5-4.5-9 8.5" />
    </Glyph>
  );
}

export function ShieldGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M12 3.5l7 2.5v5.5c0 4.4-3 7.7-7 9-4-1.3-7-4.6-7-9V6z" />
      <Path d="M9 12l2 2 4-4" />
    </Glyph>
  );
}

export function AlertGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={12} cy={12} r={8.5} />
      <Path d="M12 8v4.5M12 16h.01" />
    </Glyph>
  );
}

export function CrossGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M6.5 6.5l11 11M17.5 6.5l-11 11" />
    </Glyph>
  );
}

export function HelpGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={12} cy={12} r={8.5} />
      <Path d="M9.6 9.5a2.5 2.5 0 0 1 4.8 1c0 1.7-2.4 2.2-2.4 3.5M12 16.8h.01" />
    </Glyph>
  );
}

export function ArrowGlyph({
  back = false,
  ...props
}: GlyphProps & { back?: boolean }) {
  return (
    <Glyph {...props}>
      <Path
        d="M5 12h14M13 6l6 6-6 6"
        transform={back ? "rotate(180 12 12)" : undefined}
      />
    </Glyph>
  );
}

export function BracesGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M8.5 4H8a2 2 0 0 0-2 2v3.5A2.5 2.5 0 0 1 3.5 12 2.5 2.5 0 0 1 6 14.5V18a2 2 0 0 0 2 2h.5M15.5 4h.5a2 2 0 0 1 2 2v3.5a2.5 2.5 0 0 0 2.5 2.5 2.5 2.5 0 0 0-2.5 2.5V18a2 2 0 0 1-2 2h-.5" />
    </Glyph>
  );
}

export function BanGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={12} cy={12} r={8.5} />
      <Path d="M6 6l12 12" />
    </Glyph>
  );
}

export function CircleCheckGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={12} cy={12} r={8.5} />
      <Path d="M8.5 12.2l2.4 2.4 4.6-4.8" />
    </Glyph>
  );
}

export function CircleCrossGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={12} cy={12} r={8.5} />
      <Path d="M9.5 9.5l5 5M14.5 9.5l-5 5" />
    </Glyph>
  );
}

export function ListGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M4 6.5l1.5 1.5L8 5.5M4 13l1.5 1.5L8 12M11.5 7h8.5M11.5 13.5h8.5M11.5 19h8.5M4.5 19h2" />
    </Glyph>
  );
}

/** An open ring, spun by SpinGlyph. */
export function RingGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M20.5 12a8.5 8.5 0 1 1-6-8.1" />
    </Glyph>
  );
}

export function ReplyGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M9.5 7L4.5 12l5 5M4.5 12h10a5 5 0 0 1 5 5v1" />
    </Glyph>
  );
}

export function WrapGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M4 6.5h16M4 12h12.5a3.25 3.25 0 0 1 0 6.5H12M4 18.5h4.5M14 16.5l-2 2 2 2" />
    </Glyph>
  );
}

export function BookGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M12 6.5c-1.6-1.3-4-2-7.5-2v13c3.5 0 5.9.7 7.5 2 1.6-1.3 4-2 7.5-2v-13c-3.5 0-5.9.7-7.5 2zM12 6.5v13" />
    </Glyph>
  );
}

export function ExternalGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M14 4.5h5.5V10M19.5 4.5L11 13M17 14v4a2 2 0 0 1-2 2H6a2 2 0 0 1-2-2V9a2 2 0 0 1 2-2h4" />
    </Glyph>
  );
}

export function DoubleCheckGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Path d="M2.5 12.5l4.5 4.5 9-9.5M12 16.5l.5.5 9-9.5" />
    </Glyph>
  );
}

export function ClockGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Circle cx={12} cy={12} r={8.5} />
      <Path d="M12 7.5V12l3 2" />
    </Glyph>
  );
}

export function MicGlyph(props: GlyphProps) {
  return (
    <Glyph {...props}>
      <Rect x={9} y={3.5} width={6} height={11} rx={3} />
      <Path d="M5.5 11a6.5 6.5 0 0 0 13 0M12 17.5v3" />
    </Glyph>
  );
}

TSsrc/primitives/code-tokens.ts

import {
  normalizeTokens,
  Prism,
  type PrismTheme,
  themes,
} from "prism-react-renderer";
import { useMemo } from "react";
import { useUniwind } from "uniwind";

export type CodeLanguage =
  | "bash"
  | "css"
  | "go"
  | "javascript"
  | "json"
  | "jsx"
  | "kotlin"
  | "markdown"
  | "python"
  | "rust"
  | "sql"
  | "swift"
  | "text"
  | "tsx"
  | "typescript"
  | "yaml";

export type CodeToken = { content: string; color?: string };
export type CodeTokenLines = CodeToken[][];

// Prism's bundle has no shell grammar; this covers what agents usually run.
if (!Prism.languages.bash) {
  Prism.languages.bash = {
    comment: { pattern: /(^|\s)#.*/, lookbehind: true },
    string: { pattern: /(["'])(?:\\.|(?!\1)[^\\])*\1/, greedy: true },
    variable: /\$(?:\w+|\{[^}]+\})/,
    function: { pattern: /(^|[|;&]\s*|\$\s+)[\w./-]+/m, lookbehind: true },
    keyword:
      /\b(?:if|then|else|elif|fi|for|while|do|done|case|esac|in|function|export|return)\b/,
    property: /(^|\s)--?[\w-]+/,
    operator: /&&|\|\||[|;&<>]/,
    number: /\b\d+(?:\.\d+)?\b/,
  };
}

const LIGHT = themes.github;
const DARK = themes.oneDark;

function palette(theme: PrismTheme) {
  const colors = new Map<string, string>();
  for (const style of theme.styles) {
    const color = style.style.color;
    if (!color) continue;
    for (const type of style.types) colors.set(type, color);
  }
  return colors;
}
const PALETTES = { light: palette(LIGHT), dark: palette(DARK) };

// Small, bounded cache: streaming code re-tokenizes a growing string.
const cache = new Map<string, string[][][]>();
const CACHE_SIZE = 64;

/** Splits code into lines of tokens, each token tagged with its Prism types. */
function tokenize(code: string, language: CodeLanguage) {
  const key = `${language}\u0000${code}`;
  const hit = cache.get(key);
  if (hit) return hit;
  const grammar = language === "text" ? undefined : Prism.languages[language];
  const lines = grammar
    ? normalizeTokens(Prism.tokenize(code, grammar)).map((line) =>
        line.map((token) => [token.content, ...token.types]),
      )
    : code.split("\n").map((line) => [[line, "plain"]]);
  cache.set(key, lines);
  if (cache.size > CACHE_SIZE)
    cache.delete(cache.keys().next().value as string);
  return lines;
}

/**
 * Syntax-highlighted lines for the current light or dark theme. Tokenizing is
 * synchronous, so streamed code never flashes back to plain text.
 */
export function useCodeTokens(
  code: string,
  language: CodeLanguage,
): CodeTokenLines {
  const { theme } = useUniwind();
  const colors = theme === "dark" ? PALETTES.dark : PALETTES.light;
  return useMemo(
    () =>
      tokenize(code, language).map((line) =>
        line.map(([content = "", ...types]) => {
          let color: string | undefined;
          for (const type of types) color = colors.get(type) ?? color;
          return { content, color };
        }),
      ),
    [code, colors, language],
  );
}

TSXsrc/primitives/spin-glyph.tsx

import { useEffect } from "react";
import type { ColorValue } from "react-native";
import Animated, {
  cancelAnimation,
  Easing,
  ReduceMotion,
  useAnimatedStyle,
  useSharedValue,
  withRepeat,
  withTiming,
} from "react-native-reanimated";
import { RingGlyph } from "./agent-icons";

/**
 * A spinning ring for busy states. Reduced motion holds it still; the ring
 * still reads as "in progress".
 */
export function SpinGlyph({
  size = 16,
  color,
  reduce,
}: {
  size?: number;
  color?: ColorValue;
  reduce: boolean;
}) {
  const turn = useSharedValue(0);

  useEffect(() => {
    if (reduce) {
      cancelAnimation(turn);
      turn.value = 0;
      return;
    }
    turn.value = 0;
    turn.value = withRepeat(
      withTiming(1, {
        duration: 900,
        easing: Easing.linear,
        reduceMotion: ReduceMotion.Never,
      }),
      -1,
      false,
    );
    return () => cancelAnimation(turn);
  }, [reduce, turn]);

  const style = useAnimatedStyle(() => ({
    transform: [{ rotate: `${turn.value * 360}deg` }],
  }));

  return (
    <Animated.View style={style}>
      <RingGlyph size={size} color={color} />
    </Animated.View>
  );
}

TSsrc/styles/motion.ts

import { Easing, ReduceMotion } from "react-native-reanimated";

// Mirrors beUI's lib/ease.ts so native motion matches the web library.

export const EASE_OUT = Easing.bezier(0.16, 1, 0.3, 1);
export const EASE_IN_OUT = Easing.bezier(0.77, 0, 0.175, 1);

/** Press feedback on buttons and other tappable surfaces. */
export const SPRING_PRESS = {
  stiffness: 500,
  damping: 30,
  mass: 0.6,
  reduceMotion: ReduceMotion.System,
} as const;

/** Content swaps: label and icon slots trading places inside a control. */
export const SPRING_SWAP = {
  stiffness: 460,
  damping: 30,
  mass: 0.55,
  reduceMotion: ReduceMotion.System,
} as const;

/** Shared-layout glides: pills, indicators and panels moving between positions. */
export const SPRING_LAYOUT = {
  stiffness: 360,
  damping: 32,
  mass: 0.6,
  reduceMotion: ReduceMotion.System,
} as const;

/** Dragged handles and fills; critically damped so values never rebound off an end. */
export const SPRING_GLIDE = {
  stiffness: 700,
  damping: 50,
  mass: 0.5,
  reduceMotion: ReduceMotion.System,
} as const;

export const motion = {
  press: SPRING_PRESS,
  swap: SPRING_SWAP,
  layout: SPRING_LAYOUT,
  glide: SPRING_GLIDE,
  exit: { duration: 160, easing: EASE_OUT, reduceMotion: ReduceMotion.System },
  fade: { duration: 150, reduceMotion: ReduceMotion.System },
} as const;

4Copy the component

TSXsrc/components/code-block/code-block.tsx

import { type ReactNode, useEffect, useRef, useState } from "react";
import {
  Pressable,
  ScrollView,
  StyleSheet,
  Text,
  View,
  type ViewProps,
} from "react-native";
import Animated, {
  useAnimatedStyle,
  useSharedValue,
  withSpring,
} from "react-native-reanimated";
import { useResolveClassNames } from "uniwind";
import { useReducedMotionPreference } from "../../hooks/use-reduced-motion";
import {
  CheckGlyph,
  CopyGlyph,
  FileGlyph,
  WrapGlyph,
} from "../../primitives/agent-icons";
import {
  type CodeLanguage,
  type CodeToken,
  useCodeTokens,
} from "../../primitives/code-tokens";
import { SpinGlyph } from "../../primitives/spin-glyph";
import { SPRING_PRESS } from "../../styles/motion";

export type CodeBlockStatus = "streaming" | "complete";

const LINE = 20;
const GUTTER = 44;
const COPIED_FOR = 1600;

/** One line of tokens as nested Text, so colors stay on the line's baseline. */
export function CodeLineText({
  tokens,
  wrap,
  className = "",
}: {
  tokens: CodeToken[];
  wrap?: boolean;
  className?: string;
}) {
  return (
    <Text
      numberOfLines={wrap ? undefined : 1}
      className={`font-mono text-xs text-foreground/85 ${className}`}
      style={styles.line}
    >
      {tokens.length === 0
        ? " "
        : tokens.map((token, index) => (
            <Text
              key={index}
              style={token.color ? { color: token.color } : undefined}
            >
              {token.content}
            </Text>
          ))}
    </Text>
  );
}

function IconButton({
  label,
  selected,
  reduce,
  onPress,
  children,
}: {
  label: string;
  selected?: boolean;
  reduce: boolean;
  onPress: () => void;
  children: ReactNode;
}) {
  const scale = useSharedValue(1);
  const style = useAnimatedStyle(() => ({
    transform: [{ scale: scale.value }],
  }));
  return (
    <Pressable
      accessibilityRole="button"
      accessibilityLabel={label}
      accessibilityState={selected === undefined ? undefined : { selected }}
      hitSlop={8}
      onPress={onPress}
      onPressIn={() => {
        if (!reduce) scale.value = withSpring(0.9, SPRING_PRESS);
      }}
      onPressOut={() => {
        scale.value = withSpring(1, SPRING_PRESS);
      }}
    >
      <Animated.View style={[styles.iconButton, style]}>
        {children}
      </Animated.View>
    </Pressable>
  );
}

export type CodeBlockProps = Omit<ViewProps, "children"> & {
  code: string;
  /** Defaults to "typescript". */
  language?: CodeLanguage;
  filename?: string;
  /** Defaults to "complete". While streaming, the view follows new lines. */
  status?: CodeBlockStatus;
  /** Defaults to true. */
  showLineNumbers?: boolean;
  /** 1-based lines to tint. */
  highlightLines?: number[];
  /** Tallest the code grows before it scrolls. Defaults to 280. */
  maxHeight?: number;
  /** Starts wrapped. The header has a toggle either way. Defaults to false. */
  wrap?: boolean;
  /** Shows a copy button. Copy with your clipboard library here. */
  onCopy?: () => unknown;
  className?: string;
  disableAnimation?: boolean;
};

/**
 * Highlighted code that streams in line by line. Line numbers stay put while
 * long lines scroll sideways, and a tap wraps them instead.
 */
export function CodeBlock({
  code,
  language = "typescript",
  filename,
  status = "complete",
  showLineNumbers = true,
  highlightLines = [],
  maxHeight = 280,
  wrap: initialWrap = false,
  onCopy,
  className = "",
  disableAnimation = false,
  ...props
}: CodeBlockProps) {
  const reducedMotion = useReducedMotionPreference();
  const reduce = reducedMotion || disableAnimation;
  const streaming = status === "streaming";
  const lines = useCodeTokens(code, language);
  const [wrap, setWrap] = useState(initialWrap);
  const [copied, setCopied] = useState(false);
  const [viewport, setViewport] = useState(0);
  const copiedTimer = useRef<ReturnType<typeof setTimeout> | undefined>(
    undefined,
  );
  const scrollRef = useRef<ScrollView>(null);
  const following = useRef(true);
  const dragging = useRef(false);
  // The last lines often land with the switch to "complete", so the view
  // follows one more size change after the stream ends.
  const settling = useRef(false);
  const wasStreaming = useRef(streaming);
  if (wasStreaming.current !== streaming) {
    settling.current = !streaming;
    wasStreaming.current = streaming;
  }
  const highlighted = new Set(highlightLines);
  const { color: muted } = useResolveClassNames("text-muted");
  const { color: foreground } = useResolveClassNames("text-foreground");
  const { color: primary } = useResolveClassNames("text-primary");
  const { color: success } = useResolveClassNames("text-success");

  useEffect(() => {
    if (streaming) {
      following.current = true;
      return;
    }
    const timer = setTimeout(() => {
      settling.current = false;
    }, 500);
    return () => clearTimeout(timer);
  }, [streaming]);
  useEffect(() => () => clearTimeout(copiedTimer.current), []);

  const copy = async () => {
    await onCopy?.();
    setCopied(true);
    clearTimeout(copiedTimer.current);
    copiedTimer.current = setTimeout(() => setCopied(false), COPIED_FOR);
  };

  const tint = (index: number) =>
    highlighted.has(index + 1) ? "bg-primary/10" : "";

  const gutter = showLineNumbers ? (
    <View style={{ width: GUTTER }}>
      {lines.map((_, index) => (
        <View key={index} style={styles.gutterRow} className={tint(index)}>
          <Text
            className="font-mono text-xs text-muted/50"
            style={[styles.line, styles.tabular]}
          >
            {index + 1}
          </Text>
        </View>
      ))}
    </View>
  ) : null;

  return (
    <View
      accessibilityState={{ busy: streaming }}
      className={`w-full overflow-hidden rounded-2xl bg-surface ${className}`}
      {...props}
    >
      <View style={styles.header} className="px-3">
        <FileGlyph size={14} color={muted} />
        {filename ? (
          <Text
            numberOfLines={1}
            className="shrink font-mono text-xs text-foreground/80"
          >
            {filename}
          </Text>
        ) : null}
        <Text
          className="text-[10px] font-medium uppercase text-muted/70"
          style={styles.tracking}
        >
          {language}
        </Text>
        <View accessibilityLiveRegion="polite" style={styles.status}>
          {streaming ? (
            <SpinGlyph size={12} color={primary} reduce={reduce} />
          ) : (
            <CheckGlyph size={12} color={success} />
          )}
          <Text
            className={`text-[10px] font-medium ${streaming ? "text-primary" : "text-success"}`}
          >
            {streaming ? "Writing" : "Ready"}
          </Text>
        </View>
        <IconButton
          label="Wrap lines"
          selected={wrap}
          reduce={reduce}
          onPress={() => setWrap((value) => !value)}
        >
          <WrapGlyph size={14} color={wrap ? foreground : muted} />
        </IconButton>
        {onCopy ? (
          <IconButton
            label={copied ? "Copied" : "Copy code"}
            reduce={reduce}
            onPress={() => void copy()}
          >
            {copied ? (
              <CheckGlyph size={14} color={foreground} />
            ) : (
              <CopyGlyph size={14} color={muted} />
            )}
          </IconButton>
        ) : null}
      </View>
      {/* Padding sits outside the scroll area and its height snaps to whole
          lines, so following the stream never leaves a half line at an edge. */}
      <View className="border-t border-foreground/5 py-2">
        <ScrollView
          ref={scrollRef}
          style={{
            maxHeight: Math.max(
              LINE,
              Math.floor((maxHeight - 16) / LINE) * LINE,
            ),
          }}
          nestedScrollEnabled
          showsVerticalScrollIndicator={false}
          scrollEventThrottle={32}
          onLayout={({ nativeEvent }) => setViewport(nativeEvent.layout.width)}
          onScrollBeginDrag={() => {
            dragging.current = true;
          }}
          onMomentumScrollEnd={() => {
            dragging.current = false;
          }}
          onScrollEndDrag={({ nativeEvent }) => {
            if (!nativeEvent.velocity?.y) dragging.current = false;
          }}
          onScroll={({ nativeEvent }) => {
            if (!dragging.current) return;
            const { contentOffset, contentSize, layoutMeasurement } =
              nativeEvent;
            following.current =
              contentSize.height - contentOffset.y - layoutMeasurement.height <
              24;
          }}
          onContentSizeChange={() => {
            const follow = streaming || settling.current;
            settling.current = false;
            if (follow && following.current && !dragging.current) {
              scrollRef.current?.scrollToEnd({ animated: !reduce });
            }
          }}
        >
          <View accessibilityLiveRegion={streaming ? "polite" : "none"}>
            {wrap ? (
              // Wrapped lines vary in height, so each row carries its own number.
              lines.map((tokens, index) => (
                <View key={index} style={styles.row} className={tint(index)}>
                  {showLineNumbers ? (
                    <Text
                      className="font-mono text-xs text-muted/50"
                      style={[styles.line, styles.tabular, styles.number]}
                    >
                      {index + 1}
                    </Text>
                  ) : null}
                  <CodeLineText
                    tokens={tokens}
                    wrap
                    className={`flex-1 pr-4 ${showLineNumbers ? "pl-1" : "pl-4"}`}
                  />
                </View>
              ))
            ) : (
              <View style={styles.row}>
                {gutter}
                {/* Only the code scrolls sideways; the numbers stay in place. */}
                <ScrollView
                  horizontal
                  showsHorizontalScrollIndicator={false}
                  style={styles.flex}
                >
                  <View
                    style={{
                      minWidth: Math.max(
                        0,
                        viewport - (showLineNumbers ? GUTTER : 0),
                      ),
                    }}
                  >
                    {lines.map((tokens, index) => (
                      <View
                        key={index}
                        className={`${tint(index)} ${showLineNumbers ? "pl-1" : "pl-4"} pr-4`}
                      >
                        <CodeLineText tokens={tokens} />
                      </View>
                    ))}
                  </View>
                </ScrollView>
              </View>
            )}
          </View>
        </ScrollView>
      </View>
    </View>
  );
}

const styles = StyleSheet.create({
  flex: { flex: 1 },
  header: { flexDirection: "row", alignItems: "center", gap: 10, height: 44 },
  status: {
    flexDirection: "row",
    alignItems: "center",
    gap: 4,
    marginLeft: "auto",
  },
  iconButton: {
    width: 30,
    height: 30,
    borderRadius: 15,
    alignItems: "center",
    justifyContent: "center",
  },
  line: { lineHeight: LINE, minHeight: LINE },
  gutterRow: { height: LINE, alignItems: "flex-end", paddingRight: 12 },
  number: { width: GUTTER, textAlign: "right", paddingRight: 12 },
  row: { flexDirection: "row" },
  tabular: { fontVariant: ["tabular-nums"] },
  tracking: { letterSpacing: 0.4 },
});

TSsrc/components/code-block/index.ts

export type { CodeLanguage } from "../../primitives/code-tokens";
export type { CodeBlockProps, CodeBlockStatus } from "./code-block";
export { CodeBlock, CodeLineText } from "./code-block";

Documentation

Native port of beUI Code Block: highlighted code that an agent writes line by line.

import * as Clipboard from "expo-clipboard";
import { CodeBlock } from "./src";

<CodeBlock
  code={code}
  filename="summarize.ts"
  language="typescript"
  status={writing ? "streaming" : "complete"}
  highlightLines={[4, 5]}
  onCopy={() => Clipboard.setStringAsync(code)}
/>

Behavior

Highlighting covers TypeScript, TSX, JavaScript, JSX, JSON, Bash, Python, Swift, Kotlin, Go, Rust, SQL, CSS, YAML and Markdown, in colors that follow light and dark mode. Use "text" for none.
While status is streaming, the header says "Writing" and the view follows new lines. It says "Ready" once complete.
highlightLines tints whole rows, numbers included. showLineNumbers turns the numbers off.
Copy appears when you pass onCopy and shows a check for 1600 ms.

Better on a phone

Line numbers stay put while long lines scroll sideways, so you never lose track of which line you're on.
A button in the header wraps long lines instead, and back. Start wrapped with wrap.
Following stops the moment you drag up to read and resumes when you return to the end.
Highlighting runs in plain JavaScript as the code arrives, so streamed lines never flash back to plain text.

Accessibility

The status is a polite live region, and the block is marked busy while streaming.
The copy and wrap buttons have names, and wrap reports whether it's on.
Reduced motion, or disableAnimation, follows without smooth scrolling and holds the spinner still.

Copy this directory, hooks/use-reduced-motion.ts, primitives/agent-icons.tsx, primitives/code-tokens.ts, primitives/spin-glyph.tsx, styles/motion.ts, and the semantic tokens in styles/theme.css. It uses react-native-svg and prism-react-renderer for tokenizing.

Also on the web. The React version of Code Block, built with Motion and Tailwind CSS.

Code Block

Preview

Install

1Install the libraries

2Add the theme tokens

3Copy the shared files

4Copy the component

Documentation

Behavior

Better on a phone

Accessibility

Related components

File Diff

Tool Result

Streaming Response