emberjs/ember.js · error · SyntaxError

A block may only be used inside an HTML element or another b

Error message

A block may only be used inside an HTML element or another block.

What it means

Error "A block may only be used inside an HTML element or another block." thrown in emberjs/ember.js.

Source

Thrown at packages/@glimmer/syntax/lib/parser/handlebars-node-visitors.ts:126

        // If the stack is not balanced, then it is likely our own bug, because
        // any unclosed Handlebars blocks should already been caught by now
        assert(poppedNode !== undefined, '[BUG] empty parser elementStack');
        assert(false, `[BUG] mismatched parser elementStack node: ${node.type}`);
      }
    }

    return node;
  }

  BlockStatement(block: HBS.UpstreamBlockStatement): ASTv1.BlockStatement | void {
    if (this.tokenizer.state === 'comment') {
      assert(block.loc, '[BUG] BlockStatement in parser unexpectedly did not have loc');
      this.appendToCommentData(this.sourceForNode(block as HBS.Node));
      return;
    }

    if (this.tokenizer.state !== 'data' && this.tokenizer.state !== 'beforeData') {
      throw generateSyntaxError(
        'A block may only be used inside an HTML element or another block.',
        this.source.spanFor(block.loc)
      );
    }

    const { path, params, hash } = acceptCallNodes(this, block);
    const loc = this.source.spanFor(block.loc);

    // Backfill block params loc for the default block
    let blockParams: ASTv1.VarHead[] = [];
    let repairedBlock: HBS.BlockStatement;

    if (block.program.blockParams?.length) {
      // Start from right after the hash
      let span = hash.loc.collapse('end');

      // Extend till the beginning of the block
      if (block.program.loc) {

View on GitHub (pinned to 26f97246a8)

When it happens

Trigger: Thrown at packages/@glimmer/syntax/lib/parser/handlebars-node-visitors.ts:126 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of emberjs/ember.js@26f97246a8 (2026-09-01). Data as JSON: /api/errors/1d86ae0094d14af2. Report an issue: GitHub.