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3c4a065 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 | // The host renderer. It knows nine node kinds and nothing else: no bindings,
// no state, no effect semantics. Everything it draws was resolved by the WASM
// runtime, and every interaction goes straight back to it.
/**
* @param {HTMLElement} mount
* @param {object} runtime the WASM Runtime
* @param {() => void} onChange called after any state-mutating interaction
*/
export function paint(mount, runtime, onChange) {
const focus = captureFocus(mount);
mount.replaceChildren();
let tree;
try {
tree = JSON.parse(runtime.render());
} catch (err) {
mount.append(note(`render failed: ${err.message}`));
return;
}
if (tree.length === 0) {
mount.append(note('empty view'));
}
for (const node of tree) {
mount.append(build(node, runtime, onChange));
}
restoreFocus(mount, focus);
}
function build(node, runtime, onChange) {
switch (node.kind) {
case 'col':
case 'row':
case 'list':
case 'if':
return container(node, runtime, onChange);
case 'sp':
return el('div', 'p-sp');
case 'txt': {
const p = el('p', 'p-txt');
p.textContent = node.text ?? '';
return p;
}
case 'btn': {
const b = el('button', 'p-btn');
b.textContent = node.text ?? '';
b.title = node.effect ?? '';
b.addEventListener('click', () => {
// A failed effect is a runtime type error, not a crash: report and
// leave the state alone.
try {
runtime.dispatch(node.effect);
} catch (err) {
console.warn('effect refused:', node.effect, err);
}
onChange();
});
return b;
}
case 'in': {
const input = el('input', 'p-in');
input.type = 'text';
input.value = node.value ?? '';
input.dataset.field = node.field;
if (node.placeholder) input.placeholder = node.placeholder;
input.addEventListener('input', () => {
runtime.set_text(node.field, input.value);
onChange();
});
return input;
}
case 'chk': {
const label = el('label', 'p-chk');
const box = el('input');
box.type = 'checkbox';
box.checked = Boolean(node.checked);
box.dataset.field = node.field;
box.addEventListener('change', () => {
runtime.set_bool(node.field, box.checked);
onChange();
});
label.append(box, document.createTextNode(node.text ?? ''));
return label;
}
default:
return note(`unknown kind: ${node.kind}`);
}
}
function container(node, runtime, onChange) {
const box = el('div', `p-${node.kind}`);
for (const child of node.children ?? []) {
box.append(build(child, runtime, onChange));
}
return box;
}
function el(tag, className) {
const node = document.createElement(tag);
if (className) node.className = className;
return node;
}
function note(text) {
const p = el('p', 'p-empty');
p.textContent = text;
return p;
}
// Repainting the whole tree on every keystroke is fine at this size, but it
// would throw away the caret. Put it back where it was.
function captureFocus(mount) {
const active = document.activeElement;
if (!active || !mount.contains(active) || !active.dataset?.field) return null;
return {
field: active.dataset.field,
start: active.selectionStart,
end: active.selectionEnd,
};
}
function restoreFocus(mount, focus) {
if (!focus) return;
// Field names are `[a-z][a-z0-9_]*` by grammar, so they need no escaping.
const next = mount.querySelector(`[data-field="${focus.field}"]`);
if (!next) return;
next.focus();
if (typeof next.setSelectionRange === 'function' && focus.start !== null) {
try {
next.setSelectionRange(focus.start, focus.end);
} catch {
// Checkboxes have no selection range; nothing to restore.
}
}
}
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