Method expandOnce

static/katex/katex.mjs:13987–14039

* Expand the next token only once if possible. * * If the token is expanded, the resulting tokens will be pushed onto * the stack in reverse order and will be returned as an array, * also in reverse order. * * If not, the next token will be returned without removing it * from th

()

  expandOnce() {
    const topToken = this.popToken();
    const name = topToken.text;

    const expansion = this._getExpansion(name);

    if (expansion == null) {
      // mainly checking for undefined here
      // Fully expanded
      this.pushToken(topToken);
      return topToken;
    }

    this.expansionCount++;

    if (this.expansionCount > this.settings.maxExpand) {
      throw new ParseError("Too many expansions: infinite loop or " + "need to increase maxExpand setting");
    }

    let tokens = expansion.tokens;

    if (expansion.numArgs) {
      const args = this.consumeArgs(expansion.numArgs); // paste arguments in place of the placeholders

      tokens = tokens.slice(); // make a shallow copy

      for (let i = tokens.length - 1; i >= 0; --i) {
        let tok = tokens[i];

        if (tok.text === "#") {
          if (i === 0) {
            throw new ParseError("Incomplete placeholder at end of macro body", tok);
          }

          tok = tokens[--i]; // next token on stack

          if (tok.text === "#") {
            // ## → #
            tokens.splice(i + 1, 1); // drop first #
          } else if (/^[1-9]$/.test(tok.text)) {
            // replace the placeholder with the indicated argument
            tokens.splice(i, 2, ...args[+tok.text - 1]);
          } else {
            throw new ParseError("Not a valid argument number", tok);
          }
        }
      }
    } // Concatenate expansion onto top of stack.


    this.pushTokens(tokens);
    return tokens;
  }
  /**
   * Expand the next token only once (if possible), and return the resulting
   * top token on the stack (without removing anything from the stack).