handlebars-lang/handlebars.js · error · Exception

Template was precompiled with an older version of Handlebars

Error message

Template was precompiled with an older version of Handlebars than the current runtime. Please update your precompiler to a newer version (${runtimeVersions}) or downgrade your runtime to an older version (${compilerVersions}).

What it means

Precompiled Handlebars templates embed a compiler revision (COMPILER_REVISION). At load time the runtime's `checkRevision` compares the template's revision against the runtime's revision and the minimum compatible revision (LAST_COMPATIBLE_COMPILER_REVISION). If the template's revision is older than the minimum the runtime supports, it throws this Exception because the template data format can no longer be trusted.

Source

Thrown at lib/handlebars/runtime.js:30

  createProtoAccessControl,
  resultIsAllowed,
} from './internal/proto-access.js';

export function checkRevision(compilerInfo) {
  const compilerRevision = (compilerInfo && compilerInfo[0]) || 1,
    currentRevision = COMPILER_REVISION;

  if (
    compilerRevision >= LAST_COMPATIBLE_COMPILER_REVISION &&
    compilerRevision <= COMPILER_REVISION
  ) {
    return;
  }

  if (compilerRevision < LAST_COMPATIBLE_COMPILER_REVISION) {
    const runtimeVersions = REVISION_CHANGES[currentRevision],
      compilerVersions = REVISION_CHANGES[compilerRevision];
    throw new Exception(
      'Template was precompiled with an older version of Handlebars than the current runtime. ' +
        'Please update your precompiler to a newer version (' +
        runtimeVersions +
        ') or downgrade your runtime to an older version (' +
        compilerVersions +
        ').'
    );
  } else {
    // Use the embedded version info since the runtime doesn't know about this revision yet
    throw new Exception(
      'Template was precompiled with a newer version of Handlebars than the current runtime. ' +
        'Please update your runtime to a newer version (' +
        compilerInfo[1] +
        ').'
    );
  }
}

View on GitHub (pinned to 13a7a67991)

Solutions

1. Re-precompile all templates with the current handlebars version (`handlebars templates/ -f compiled.js`) so COMPILER_REVISION matches the runtime
2. If re-precompiling is impossible, downgrade the handlebars runtime package to a version within the range printed in the error message
3. Clear build/CI caches so freshly compiled templates are deployed
4. Pin the compiler and runtime to the same handlebars version in package.json/lockfile

Example fix

// before: stale precompiled template from old compiler
// templates/compiled.js generated by handlebars 1.3, runtime is 4.7
import compiled from './templates/compiled.js';

// after: regenerate with the installed compiler version
// npx handlebars templates/ -f templates/compiled.js
import compiled from './templates/compiled.js';

import compiledSpec from './templates/compiled.js';
import Handlebars from 'handlebars/runtime';

function assertTemplateCompatible(spec) {
  const compilerRevision = spec.compiler?.[0];
  if (compilerRevision < 7) { // LAST_COMPATIBLE_COMPILER_REVISION for hb 4.x
    throw new Error('Template precompiled by unsupported old Handlebars; recompile it');
  }
}
assertTemplateCompatible(compiledSpec);
Handlebars.template(compiledSpec);

function isCompatibleSpec(spec) {
  return spec && typeof spec === 'object' &&
    Array.isArray(spec.compiler) && spec.compiler[0] >= 7;
}

try {
  const tmpl = Handlebars.template(compiledSpec);
} catch (e) {
  if (e.message.includes('precompiled with an older version')) {
    throw new Error('Re-run the precompiler: npx handlebars templates/ -f templates/compiled.js');
  }
  throw e;
}

When it happens

Trigger: `checkRevision` is called during template load and `compilerRevision < LAST_COMPATIBLE_COMPILER_REVISION`, i.e. a template precompiled by a Handlebars compiler old enough that the current runtime no longer accepts its format.

Common situations: Upgrading the handlebars runtime dependency without re-running the precompiler; templates checked into the repo were generated years ago by handlebars 1.x/2.x while the app now runs handlebars 4.x; a build cache served stale precompiled template files.

Related errors

• Template was precompiled with a newer version of Handlebars
• No environment passed to template
• Unknown template object: ${typeof templateSpec}
• The partial ${options.name} could not be compiled when runni
• Invalid stack pop

AI-assisted analysis of handlebars-lang/handlebars.js@13a7a67991 (2026-09-02). Data as JSON: /api/errors/971dd21632dd6337. Report an issue: GitHub.