Function buildExpression

src/buildHTML.ts:59–134

(
    expression: AnyParseNode[],
    options: Options,
    isRealGroup: boolean | "root",
    surrounding: [DomType | null | undefined, DomType | null | undefined] = [null, null],
)

 * consisting type of nodes that will be added to the left and right.
 */
export const buildExpression = function(
    expression: AnyParseNode[],
    options: Options,
    isRealGroup: boolean | "root",
    surrounding: [DomType | null | undefined, DomType | null | undefined] = [null, null],
): HtmlDomNode[] {
    // Parse expressions into `groups`.
    const groups: HtmlDomNode[] = [];
    for (let i = 0; i < expression.length; i++) {
        const output = buildGroup(expression[i], options);
        if (output instanceof DocumentFragment) {
            const children: ReadonlyArray<HtmlDomNode> = output.children;
            groups.push(...children);
        } else {
            groups.push(output);
        }
    }

    // Combine consecutive domTree.symbolNodes into a single symbolNode.
    tryCombineChars(groups);

    // If `expression` is a partial group, let the parent handle spacings
    // to avoid processing groups multiple times.
    if (!isRealGroup) {
        return groups;
    }

    let glueOptions = options;
    if (expression.length === 1) {
        const node = expression[0];
        if (node.type === "sizing") {
            glueOptions = options.havingSize(node.size);
        } else if (node.type === "styling") {
            glueOptions = options.havingStyle(styleMap[node.style]);
        }
    }

    // Dummy spans for determining spacings between surrounding atoms.
    // If `expression` has no atoms on the left or right, class "leftmost"
    // or "rightmost", respectively, is used to indicate it.
    const dummyPrev = makeSpan([surrounding[0] || "leftmost"], [], options);
    const dummyNext = makeSpan([surrounding[1] || "rightmost"], [], options);

    // TODO: These code assumes that a node's math class is the first element
    // of its `classes` array. A later cleanup should ensure this, for
    // instance by changing the signature of `makeSpan`.

    // Before determining what spaces to insert, perform bin cancellation.
    // Binary operators change to ordinary symbols in some contexts.
    const isRoot = (isRealGroup === "root");
    traverseNonSpaceNodes(groups, (node, prev): void => {
        const prevType = prev.classes[0];
        const type = node.classes[0];
        if (prevType === "mbin" && binRightCanceller.has(type)) {
            prev.classes[0] = "mord";
        } else if (type === "mbin" && binLeftCanceller.has(prevType)) {
            node.classes[0] = "mord";
        }