Method parse

www/js/_hyperscript.js:9793–9818

* Parse when feature * @param {Parser} parser * @returns {WhenFeature | undefined}

(parser)

     * @returns {WhenFeature | undefined}
     */
    static parse(parser) {
      if (!parser.matchToken("when")) return;
      var exprs = [];
      do {
        parser.pushFollow("or");
        try {
          exprs.push(parser.requireElement("expression"));
        } finally {
          parser.popFollow();
        }
      } while (parser.matchToken("or"));
      for (var i = 0; i < exprs.length; i++) {
        var expr = exprs[i];
        if (expr.type === "symbol" && expr.scope === "local" && !expr.name.startsWith("$") && !expr.name.startsWith(":")) {
          parser.raiseError(
            "Cannot watch local variable '" + expr.name + "'. Local variables are not reactive. Use '$" + expr.name + "' (global) or ':" + expr.name + "' (element-scoped) instead."
          );
        }
      }
      parser.requireToken("changes");
      var start = parser.requireElement("commandList");
      parser.ensureTerminated(start);
      var feature = new _WhenFeature(exprs, start);
      parser.setParent(start, feature);
      return feature;
    }
    constructor(exprs, start) {
      super();
      this.exprs = exprs;