Handlebars {{#each}}: Architecture for Iteration, Context Scoping, and Empty States

Requirements for Collection Rendering

A list view needs to iterate arrays or plain objects, render a meaningful empty state when no data exists, allow child expressions to reference the current item without ambiguity, and permit controlled access to the parent scope when the item alone is insufficient. Handlebars addresses these through the {{#each}} block helper, but the helper only stays maintainable if you decide deliberately what belongs in the template and what stays in application code.

The practical takeaway: bind each item explicitly with as |item|, use {{else}} for empty states, and treat the template as a presentation boundary that receives normalized collections.

Smallest Suitable Design

The minimal pattern uses {{#each}} with an explicit block variable and an {{else}} section.

{{#each orders as |order|}}
  <div class="order">
    <span>{{order.id}}</span>
    <span>{{order.total}}</span>
  </div>
{{else}}
  <p>No orders to display.</p>
{{/each}}

Without as |order|, each item becomes the current context implicitly. That works for flat properties, but it becomes ambiguous when items contain nested objects or when you need to reference the parent. The as |order| syntax names the iteration variable and preserves the parent context so ../ references remain possible.

For example, if each order belongs to a customer and the customer name lives in the parent context:

{{#each orders as |order|}}
  <div>{{order.id}} — {{../customerName}}</div>
{{else}}
  <p>No orders.</p>
{{/each}}

Trust and Data Boundaries

Handlebars templates should receive data they can render, not data they must transform. The boundary rule: normalize collections in application code before passing them to the template. If the view receives null, undefined, or a scalar where an array is expected, {{#each}} will not iterate and the {{else}} block will render. That behavior is consistent, but it can mask bugs where the wrong variable was passed.

Do not use @index for external loop tracking. It is read-only and resets for each {{#each}} invocation. If ordering or pagination state must persist outside the template, track it in your application state and pass it in as a separate value.

Operational Checks

To verify behavior in a Node.js environment (Node.js 18+ assumed; Handlebars 4.x assumed), compile and render the template with known inputs.

Run the following in a Node.js script or REPL where the handlebars package is installed:

const Handlebars = require('handlebars');
const source = `
{{#each items as |item|}}
  <li>{{item}}</li>
{{else}}
  <li>empty</li>
{{/each}}
`;
const template = Handlebars.compile(source);

// Render with a populated array
const populated = template({ items: ['alpha', 'beta'] });

// Render with an empty array
const emptyArray = template({ items: [] });

// Render with null
const nullValue = template({ items: null });

Expected checks:

• populated contains two list items and does not contain the string empty.
• emptyArray contains exactly one list item with the text empty.
• nullValue behaves the same as emptyArray because {{#each}} treats null as an empty collection.

To verify context scoping, render a template that references both the item and a parent property, then confirm the parent value appears inside the block and the item value resolves correctly.

Failure Modes

• Implicit context confusion: Omitting as |item| means the current context becomes the item. If the item is a primitive like a string or number, property lookups will fail silently or render empty strings. If the item is an object, parent properties are shadowed.
• Null and undefined collections: {{#each}} treats these as empty and renders the {{else}} block. This is safe for display, but it can hide a data-loading bug where the collection was never assigned.
• Object iteration assumptions: {{#each}} can iterate plain objects, but relying on property order or expecting array methods like .length inside the block will fail. Treat object iteration as a key-value walk, not an ordered list.
• External state via @index: Attempting to read @index outside the block or mutating it produces undefined behavior. It exists only within the block invocation.

Conditions That Would Change the Design

• Large collections: If rendering thousands of items, move pagination, windowing, or virtualization into application code and pass only the visible slice to {{#each}}.
• Reactive updates: In frameworks that re-render on state change, ensure the collection reference changes when data updates so the template re-evaluates. Handlebars itself is a string-based renderer; reactivity belongs to the host environment.
• Complex nested iteration: When nested {{#each}} blocks make ../ paths brittle, consider flattening the data structure in application code or extracting a partial with an explicit context argument.
• Non-standard iteration: If you need to iterate a Map, Set, or custom iterable, convert it to an array or plain object before rendering.

This keeps the template declarative and the data contract explicit.