Elements

If / Each

<If> and <Each> are the components for conditional and repeated content. They create no native view; they decide which elements exist. Both are compiled into calls to the native renderer, which updates only what changed: <If> swaps a branch when the condition’s truthiness changes, <Each> adds, moves and removes rows by key instead of rebuilding the list.

el-control-flow.tsx Edit in Playground Open in new tab

import { mount, signal, Text, View } from "nsh";

interface Todo {
  id: number;
  title: string;
  done: boolean;
}

let nextId = 4;

function App() {
  const todos = signal<Todo[]>([
    { id: 1, title: "Read the elements page", done: true },
    { id: 2, title: "Try <If> and <Each>", done: false },
    { id: 3, title: "Ship the app", done: false },
  ]);
  const showDone = signal(true);
  const visible = () => (showDone() ? todos() : todos().filter((t) => !t.done));
  const toggle = (id: number) => todos.update((list) => list.map((t) => (t.id === id ? { ...t, done: !t.done } : t)));
  const add = () => todos.update((list) => [...list, { id: nextId++, title: `Task ${nextId - 1}`, done: false }]);
  const remove = (id: number) => todos.update((list) => list.filter((t) => t.id !== id));
  const button = { borderRadius: 8, paddingHorizontal: 12, paddingVertical: 8 } as const;

  return (
    <View style={{ flex: 1, backgroundColor: "#f6f8fa", padding: 20, paddingTop: 24, gap: 12 }}>
      <Text style={{ fontSize: 22, fontWeight: "700", color: "#1f2328" }}>if / each</Text>
      <View style={{ flexDirection: "row", gap: 8 }}>
        <View onPress={add} activeOpacity={0.6} style={{ ...button, backgroundColor: "#1f883d" }}>
          <Text style={{ color: "#ffffff" }}>Add</Text>
        </View>
        <View onPress={() => showDone.set(!showDone())} activeOpacity={0.6} style={{ ...button, backgroundColor: "#ddf4ff" }}>
          <Text style={{ color: "#0969da" }}>{showDone() ? "Hide done" : "Show done"}</Text>
        </View>
      </View>

      <If
        when={visible().length > 0}
        else={<Text style={{ color: "#6e7781", textAlign: "center", marginTop: 40 }}>Nothing to show.</Text>}
      >
        <View style={{ gap: 8 }}>
          <Each of={visible()} key={(t: Todo) => t.id}>
            {(todo, index) => (
              <View
                style={{
                  flexDirection: "row",
                  alignItems: "center",
                  gap: 12,
                  backgroundColor: "#ffffff",
                  borderRadius: 10,
                  padding: 12,
                  borderWidth: 1,
                  borderColor: "#d0d7de",
                }}
              >
                <View
                  onPress={() => toggle(todo().id)}
                  hitSlop={8}
                  style={{
                    width: 22,
                    height: 22,
                    borderRadius: 11,
                    borderWidth: 2,
                    borderColor: "#1f883d",
                    backgroundColor: todo().done ? "#1f883d" : "transparent",
                  }}
                />
                <Text
                  style={{
                    flex: 1,
                    color: todo().done ? "#8c959f" : "#1f2328",
                    textDecorationLine: todo().done ? "line-through" : "none",
                  }}
                >
                  {index() + 1}. {todo().title}
                </Text>
                <If when={todo().done}>
                  <View onPress={() => remove(todo().id)} hitSlop={8}>
                    <Text style={{ color: "#cf222e" }}>Remove</Text>
                  </View>
                </If>
              </View>
            )}
          </Each>
        </View>
      </If>
      <Text style={{ fontSize: 12, color: "#6e7781" }}>
        {todos().filter((t) => t.done).length} of {todos().length} done
      </Text>
    </View>
  );
}

mount(App);

<View>
  <If when={user()} else={<Text>Signed out</Text>}>
    <Text>Hello, {user()!.name}</Text>
  </If>
  <Each of={todos()}>{(todo) => <Text>{todo().title}</Text>}</Each>
</View>

They are globals: they need no import (a binding of the same name in scope takes their place). Inside JSX expressions you can still use plain JavaScript (cond ? a : b, items.map(…)), but those rebuild their elements every time what they read changes; <If> and <Each> keep the elements that stay.

#`<If>`

Renders its children while when is truthy, else the else element (or nothing).

Prop	Type	Description
`when`	`unknown`	The condition. Only its truthiness matters.
`else`	`JSX.Element`	Rendered while `when` is falsy.
`children`	`JSX.Element`	Rendered while `when` is truthy.

The branch is created again only when the truthiness of when changes. A when that goes from one truthy value to another (user() changing from one object to another) keeps the branch, and the expressions inside it update on their own.

const loading = signal(true);

<If when={!loading()} else={<Text style={{ color: "#6e7781" }}>Loading…</Text>}>
  <Profile />
</If>;

#`<Each>`

Renders children(item, index) for each item of of.

Prop	Type	Description
`of`	`readonly any[] \| null \| undefined`	The items. `null` and `undefined` render nothing.
`key`	`(item: any) => unknown`	The identity of an item. Default: the item itself (objects by identity, primitives by value).
`children`	`(item: () => any, index: () => number) => JSX.Element`	Renders one row.

The row function gets accessors, not values: call item() and index(). When of changes, rows whose key is still there are kept (and moved if their position changed); their item() and index() update, and only the expressions reading them run again. New keys get new rows; rows whose key is gone are removed.

interface Todo {
  id: number;
  title: string;
  done: boolean;
}

const todos = signal<Todo[]>([]);

<Each of={todos()} key={(t: Todo) => t.id}>
  {(todo, index) => (
    <View style={{ flexDirection: "row", gap: 8 }}>
      <Text>{index() + 1}.</Text>
      <Text style={{ textDecorationLine: todo().done ? "line-through" : "none" }}>{todo().title}</Text>
    </View>
  )}
</Each>;

#Choosing a key

Items replaced by new objects on every update (immutable updates, { ...t, done: true }) need a key, usually an id. Without it each new object is a new row and its elements are created again.
Arrays of strings or numbers work without a key: they are compared by value.
Each row has its own owner: effects and cleanups created in a row end when the row is removed.

#`<Each>` or a list

<Each> creates every row. That is right for tens or a few hundred items, in a <View> or a <Scroll>. For long or unbounded data, use a list: it creates only the rows near the viewport and recycles them.

See JSX and components and reactivity for how expressions update.

#<If>

#<Each>

#Choosing a key

#<Each> or a list

#`<If>`

#`<Each>`

#`<Each>` or a list