svelte
Version:
Cybernetically enhanced web apps
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JavaScript
/**
* Map of elements that have certain elements that are not allowed inside them, in the sense that they will auto-close the parent/ancestor element.
* Theoretically one could take advantage of it but most of the time it will just result in confusing behavior and break when SSR'd.
* There are more elements that are invalid inside other elements, but they're not auto-closed and so don't break SSR and are therefore not listed here.
* @type {Record<string, { direct: string[]} | { descendant: string[]; reset_by?: string[] }>}
*/
const autoclosing_children = {
// based on http://developers.whatwg.org/syntax.html#syntax-tag-omission
li: { direct: ['li'] },
// https://developer.mozilla.org/en-US/docs/Web/HTML/Element/dt#technical_summary
dt: { descendant: ['dt', 'dd'], reset_by: ['dl'] },
dd: { descendant: ['dt', 'dd'], reset_by: ['dl'] },
p: {
descendant: [
'address',
'article',
'aside',
'blockquote',
'div',
'dl',
'fieldset',
'footer',
'form',
'h1',
'h2',
'h3',
'h4',
'h5',
'h6',
'header',
'hgroup',
'hr',
'main',
'menu',
'nav',
'ol',
'p',
'pre',
'section',
'table',
'ul'
]
},
rt: { descendant: ['rt', 'rp'] },
rp: { descendant: ['rt', 'rp'] },
optgroup: { descendant: ['optgroup'] },
option: { descendant: ['option', 'optgroup'] },
thead: { direct: ['tbody', 'tfoot'] },
tbody: { direct: ['tbody', 'tfoot'] },
tfoot: { direct: ['tbody'] },
tr: { direct: ['tr', 'tbody'] },
td: { direct: ['td', 'th', 'tr'] },
th: { direct: ['td', 'th', 'tr'] }
};
/**
* Returns true if the tag is either the last in the list of siblings and will be autoclosed,
* or not allowed inside the parent tag such that it will auto-close it. The latter results
* in the browser repairing the HTML, which will likely result in an error during hydration.
* @param {string} current
* @param {string} [next]
*/
export function closing_tag_omitted(current, next) {
const disallowed = autoclosing_children[current];
if (disallowed) {
if (
!next ||
('direct' in disallowed ? disallowed.direct : disallowed.descendant).includes(next)
) {
return true;
}
}
return false;
}
/**
* Map of elements that have certain elements that are not allowed inside them, in the sense that the browser will somehow repair the HTML.
* There are more elements that are invalid inside other elements, but they're not repaired and so don't break SSR and are therefore not listed here.
* @type {Record<string, { direct: string[]} | { descendant: string[]; reset_by?: string[]; only?: string[] } | { only: string[] }>}
*/
const disallowed_children = {
...autoclosing_children,
optgroup: { only: ['option', '#text'] },
// Strictly speaking, seeing an <option> doesn't mean we're in a <select>, but we assume it here
option: { only: ['#text'] },
form: { descendant: ['form'] },
a: { descendant: ['a'] },
button: { descendant: ['button'] },
h1: { descendant: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'] },
h2: { descendant: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'] },
h3: { descendant: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'] },
h4: { descendant: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'] },
h5: { descendant: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'] },
h6: { descendant: ['h1', 'h2', 'h3', 'h4', 'h5', 'h6'] },
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-inselect
select: { only: ['option', 'optgroup', '#text', 'hr', 'script', 'template'] },
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-intd
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-incaption
// No special behavior since these rules fall back to "in body" mode for
// all except special table nodes which cause bad parsing behavior anyway.
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-intd
tr: { only: ['th', 'td', 'style', 'script', 'template'] },
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-intbody
tbody: { only: ['tr', 'style', 'script', 'template'] },
thead: { only: ['tr', 'style', 'script', 'template'] },
tfoot: { only: ['tr', 'style', 'script', 'template'] },
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-incolgroup
colgroup: { only: ['col', 'template'] },
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-intable
table: {
only: ['caption', 'colgroup', 'tbody', 'thead', 'tfoot', 'style', 'script', 'template']
},
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-inhead
head: {
only: [
'base',
'basefont',
'bgsound',
'link',
'meta',
'title',
'noscript',
'noframes',
'style',
'script',
'template'
]
},
// https://html.spec.whatwg.org/multipage/semantics.html#the-html-element
html: { only: ['head', 'body', 'frameset'] },
frameset: { only: ['frame'] },
'#document': { only: ['html'] }
};
/**
* Returns an error message if the tag is not allowed inside the ancestor tag (which is grandparent and above) such that it will result
* in the browser repairing the HTML, which will likely result in an error during hydration.
* @param {string} child_tag
* @param {string[]} ancestors All nodes starting with the parent, up until the ancestor, which means two entries minimum
* @param {string} [child_loc]
* @param {string} [ancestor_loc]
* @returns {string | null}
*/
export function is_tag_valid_with_ancestor(child_tag, ancestors, child_loc, ancestor_loc) {
if (child_tag.includes('-')) return null; // custom elements can be anything
const ancestor_tag = ancestors[ancestors.length - 1];
const disallowed = disallowed_children[ancestor_tag];
if (!disallowed) return null;
if ('reset_by' in disallowed && disallowed.reset_by) {
for (let i = ancestors.length - 2; i >= 0; i--) {
const ancestor = ancestors[i];
if (ancestor.includes('-')) return null; // custom elements can be anything
// A reset means that forbidden descendants are allowed again
if (disallowed.reset_by.includes(ancestors[i])) {
return null;
}
}
}
if ('descendant' in disallowed && disallowed.descendant.includes(child_tag)) {
const child = child_loc ? `\`<${child_tag}>\` (${child_loc})` : `\`<${child_tag}>\``;
const ancestor = ancestor_loc
? `\`<${ancestor_tag}>\` (${ancestor_loc})`
: `\`<${ancestor_tag}>\``;
return `${child} cannot be a descendant of ${ancestor}`;
}
return null;
}
/**
* Returns an error message if the tag is not allowed inside the parent tag such that it will result
* in the browser repairing the HTML, which will likely result in an error during hydration.
* @param {string} child_tag
* @param {string} parent_tag
* @param {string} [child_loc]
* @param {string} [parent_loc]
* @returns {string | null}
*/
export function is_tag_valid_with_parent(child_tag, parent_tag, child_loc, parent_loc) {
if (child_tag.includes('-') || parent_tag?.includes('-')) return null; // custom elements can be anything
if (parent_tag === 'template') return null; // no errors or warning should be thrown in immediate children of template tags
const disallowed = disallowed_children[parent_tag];
const child = child_loc ? `\`<${child_tag}>\` (${child_loc})` : `\`<${child_tag}>\``;
const parent = parent_loc ? `\`<${parent_tag}>\` (${parent_loc})` : `\`<${parent_tag}>\``;
if (disallowed) {
if ('direct' in disallowed && disallowed.direct.includes(child_tag)) {
return `${child} cannot be a direct child of ${parent}`;
}
if ('descendant' in disallowed && disallowed.descendant.includes(child_tag)) {
return `${child} cannot be a child of ${parent}`;
}
if ('only' in disallowed && disallowed.only) {
if (disallowed.only.includes(child_tag)) {
return null;
} else {
return `${child} cannot be a child of ${parent}. \`<${parent_tag}>\` only allows these children: ${disallowed.only.map((d) => `\`<${d}>\``).join(', ')}`;
}
}
}
// These tags are only valid with a few parents that have special child
// parsing rules - if we're down here, then none of those matched and
// so we allow it only if we don't know what the parent is, as all other
// cases are invalid (and we only get into this function if we know the parent).
switch (child_tag) {
case 'body':
case 'caption':
case 'col':
case 'colgroup':
case 'frameset':
case 'frame':
case 'head':
case 'html':
return `${child} cannot be a child of ${parent}`;
case 'thead':
case 'tbody':
case 'tfoot':
return `${child} must be the child of a \`<table>\`, not a ${parent}`;
case 'td':
case 'th':
return `${child} must be the child of a \`<tr>\`, not a ${parent}`;
case 'tr':
return `\`<tr>\` must be the child of a \`<thead>\`, \`<tbody>\`, or \`<tfoot>\`, not a ${parent}`;
}
return null;
}