For the complete documentation index, see llms.txt. This page is also available as Markdown.

Advanced templating (Handlebars)

Using the Handlebar templating engine to create advanced templates

Personalizing templates with Handlebars

By default, Lob uses a basic templating engine based on Mustache. If you would like to render complex personalizations, use the alternate Handlebars templating engine route through Lob API. Handlebars syntax allows you to populate, evaluate, and iterate using templates and API requests. The biggest advantage of this approach is quickly creating dynamic personalization without making any changes to your codebase. We can use advanced templating to make dynamic tables.

Creating a template

  1. Start with any Handlebars-friendly template. Dynamic variables should be wrapped in double curly braces {{like_this}} . To the right is an example of a simple handlebars template.

<html>
Name is: {{user.name}}
Location is: {{user.location}} 
</html>
  1. To push your template to a Lob environment, use the /v1/templates API. Creating Handlebars templates via the Dashboard UI is not supported at this time. To specify that our service should use the Handlebars templating engine, you will need pass handlebars in the template request engine field as shown on the right.

POST 
	[/v1/templates](<https://api.lob.com/v1/templates>)/ 

{
"description":"Test Template",
"html":"<html>Name is: {{user.name}} <br> 
Location is: {{user.location}} </html>",
"engine":"handlebars",
"required_vars": ["user"] //optional
}

Response

{
    "id": "tmpl_81ff8f64ce61285",
....
}

Note the optional field, required_vars. Any request to create a mailpiece using this template will require the variables listed there in order to complete successfully.

Template compilation API

You can use this newly created endpoint to test that your Handlebars template compiles as expected. To do that, use the /v1/templates/ endpoint and add your merge variable(s) as a dynamic URL query parameter. You can use this to inspect how your template will display with the merge variables passed in. The response is the same format that Lob will use to render your mailpiece.

Create a mailpiece using Handlebars

Now that your template has been created in a Lob environment, the templating engine has been set to handlebars, and you've tested out your template using the Template Compilation API, you can send a mailpiece request to the /v1/checks/, /v1/postcards/, /v1/letters/ or /v1/self_mailers/ endpoint as you normally would. In the request message body, use the merge_variables field to pass in dynamic values.

Helpers

Built in helpers

The below helpers can be used for many dynamic use cases. Helpers like if blocks can include nested built-in and customer helper conditionals (like if, and, or, eq, etc).

#if

You can use the if helper to conditionally render a block. If its argument returns false, undefined, null, "", 0, or [], Handlebars will not render the block.

When you pass the following input to the above template:

This will produce the result as below:

If the input is an empty JSONObject {}, then author will become undefined and if condition fails, resulting in the output as follow:

When using a block expression, you can specify a template section to run if the expression returns a falsey value. The section, marked by else is called an "else section".

#unless

You can use the unless helper as the inverse of the if helper. Its block will be rendered if the expression returns a falsy value.

If looking up license under the current context returns a falsy value, Handlebars will render the warning. Otherwise, it will render nothing.

#each

You can iterate over a list using the built-in each helper. Inside the block, you can use this to reference the element being iterated over.

when used with this context:

will result in:

You can use the this expression in any context to reference the current context.

You can optionally provide an else section which will display only when the list is empty.

When looping through items in each, you can optionally reference the current loop index via {{@index}}.

Additionally for object iteration, {{@key}} references the current key name:

The first and last steps of iteration are noted via the @first and @last variables when iterating over an array. When iterating over an object only the @first is available. Nested each blocks may access the iteration variables via depth based paths. To access the parent index, for example, {{@../index}} can be used.

#with

The with-helper allows you to change the evaluation context of template-part.

when used with this context:

will result in:

with can also be used with block parameters to define known references in the current block. The example above can be converted to

Which allows for complex templates to potentially provide clearer code than ../ depthed references allow for.

You can optionally provide an {{else}} section which will display only when the passed value is empty.

#lookup

The lookup helper allows for dynamic parameter resolution using Handlebars variables.

This is useful for resolving values for array indexes.

It can also be used to lookup properties of object based on data from the input. The following is a more complex example that uses lookup in a sub-expression to change the evaluation contextto another object based on a property-value.

Custom helpers

Custom helpers are additional functions that can assist in the formatting of your document. The documentation here is directly pulled from the associated third-party github repo. The helpers below are supported.

For uniformity with Handlebars' terminology, we use the wordfalsey instead of the more commonly used falsy.

Array helpers

{{after}}

Returns all of the items in an array after the specified index. Opposite of before.

Params

  • array {Array}: Collection

  • n {Number}: Starting index (number of items to exclude)

  • returns {Array}: Array exluding n items.

Example

{{arrayify}}

Cast the given value to an array.

Params

  • value {any}

  • returns {Array}

Example

{{before}}

Return all of the items in the collection before the specified count. Opposite of after.

Params

  • array {Array}

  • n {Number}

  • returns {Array}: Array excluding items after the given number.

Example

{{eachIndex}}

Implementation of the default Handlebars loop helper {{#each}} adding index (0-based index) to the loop content

Params

  • array {Array}

  • options {Object}

  • returns {String}

Example

{{filter}}

Block helper that filters the given array and renders the block for values that evaluate to true, otherwise the inverse block is returned.

Params

  • array {Array}

  • value {any}

  • options {Object}

  • returns {String}

Example

{{first}}

Returns the first item, or first n items of an array.

Params

  • array {Array}

  • n {Number}: Number of items to return, starting at 0.

  • returns {Array}

Example

{{forEach}}

Iterates over each item in an array and exposes the current item in the array as context to the inner block. In addition to the current array item, the helper exposes the following variables to the inner block:

  • index

  • total

  • isFirst

  • isLast Also, @index is exposed as a private variable, and additional private variables may be defined as hash arguments.

Params

  • array {Array}

  • returns {String}

Example

{{inArray}}

Block helper that renders the block if an array has the given value. Optionally specify an inverse block to render when the array does not have the given value.

Params

  • array {Array}

  • value {any}

  • options {Object}

  • returns {String}

Example

{{isArray}}

Returns true if value is an es5 array.

Params

  • value {any}: The value to test.

  • returns {Boolean}

Example

{{itemAt}}

Returns the item from array at index idx.

Params

  • array {Array}

  • idx {Number}

  • returns {any} value

Example

{{join}}

Join all elements of array into a string, optionally using a given separator.

Params

  • array {Array}

  • separator {String}: The separator to use. Defaults to ,.

  • returns {String}

Example

{{equalsLength}}

Returns true if the the length of the given value is equal to the given length. Can be used as a block or inline helper.

Params

  • value {Array|String}

  • length {Number}

  • options {Object}

  • returns {String}

{{last}}

Returns the last item, or last n items of an array or string. Opposite of first.

Params

  • value {Array|String}: Array or string.

  • n {Number}: Number of items to return from the end of the array.

  • returns {Array}

Example

{{length}}

Returns the length of the given string or array.

Params

  • value {Array|Object|String}

  • returns {Number}: The length of the value.

Example

{{map}}

Returns a new array, created by calling function on each element of the given array. For example,

Params

  • array {Array}

  • fn {Function}

  • returns {String}

Example

{{pluck}}

Map over the given object or array or objects and create an array of values from the given prop. Dot-notation may be used (as a string) to get nested properties.

Params

  • collection {Array|Object}

  • prop {Function}

  • returns {String}

Example

{{reverse}}

Reverse the elements in an array, or the characters in a string.

Params

  • value {Array|String}

  • returns {Array|String}: Returns the reversed string or array.

Example

{{some}}

Block helper that returns the block if the callback returns true for some value in the given array.

Params

  • array {Array}

  • iter {Function}: Iteratee

  • {Options}: Handlebars provided options object

  • returns {String}

Example

{{sort}}

Sort the given array. If an array of objects is passed, you may optionally pass a key to sort on as the second argument. You may alternatively pass a sorting function as the second argument.

Params

  • array {Array}: the array to sort.

  • key {String|Function}: The object key to sort by, or sorting function.

Example

{{sortBy}}

Sort an array. If an array of objects is passed, you may optionally pass a key to sort on as the second argument. You may alternatively pass a sorting function as the second argument.

Params

  • array {Array}: the array to sort.

  • props {String|Function}: One or more properties to sort by, or sorting functions to use.

Example

{{withAfter}}

Use the items in the array after the specified index as context inside a block. Opposite of withBefore.

Params

  • array {Array}

  • idx {Number}

  • options {Object}

  • returns {Array}

Example

{{withBefore}}

Use the items in the array before the specified index as context inside a block. Opposite of withAfter.

Params

  • array {Array}

  • idx {Number}

  • options {Object}

  • returns {Array}

Example

{{withFirst}}

Use the first item in a collection inside a handlebars block expression. Opposite of withLast.

Params

  • array {Array}

  • idx {Number}

  • options {Object}

  • returns {String}

Example

{{withGroup}}

Block helper that groups array elements by given group size.

Params

  • array {Array}: The array to iterate over

  • size {Number}: The desired length of each array "group"

  • options {Object}: Handlebars options

  • returns {String}

Example

{{withLast}}

Use the last item or n items in an array as context inside a block. Opposite of withFirst.

Params

  • array {Array}

  • idx {Number}: The starting index.

  • options {Object}

  • returns {String}

Example

{{withSort}}

Block helper that sorts a collection and exposes the sorted collection as context inside the block.

Params

  • array {Array}

  • prop {String}

  • options {Object}: Specify reverse="true" to reverse the array.

  • returns {String}

Example

{{unique}}

Block helper that return an array with all duplicate values removed. Best used along with a each helper.

Params

  • array {Array}

  • options {Object}

  • returns {Array}

Example

Comparison helpers

{{and}}

Helper that renders the block if both of the given values are truthy. If an inverse block is specified it will be rendered when falsey. Works as a block helper, inline helper or subexpression.

Params

  • a {any}

  • b {any}

  • options {Object}: Handlebars provided options object

  • returns {String}

Example

{{compare}}

Render a block when a comparison of the first and third arguments returns true. The second argument is the arithemetic operator to use. You may also optionally specify an inverse block to render when falsey.

Params

  • a {}

  • operator {}: The operator to use. Operators must be enclosed in quotes: ">", "=", "<=", and so on.

  • b {}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or if specified the inverse block is rendered if falsey.

{{contains}}

Block helper that renders the block if collection has the given value, using strict equality (===) for comparison, otherwise the inverse block is rendered (if specified). If a startIndex is specified and is negative, it is used as the offset from the end of the collection.

Params

  • collection {Array|Object|String}: The collection to iterate over.

  • value {any}: The value to check for.

  • [startIndex=0] {Number}: Optionally define the starting index.

  • options {Object}: Handlebars provided options object.

Example

{{default}}

Returns the first value that is not undefined, otherwise the "default" value is returned.

Params

  • value {any}

  • defaultValue {any}

  • returns {String}

{{eq}}

Block helper that renders a block if a is equal to b. If an inverse block is specified it will be rendered when falsey. You may optionally use the compare="" hash argument for the second value.

Params

  • a {String}

  • b {String}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

Example

{{gt}}

Block helper that renders a block if a is greater than b.

If an inverse block is specified it will be rendered when falsey. You may optionally use the compare="" hash argument for the second value.

Params

  • a {String}

  • b {String}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{gte}}

Block helper that renders a block if a is greater than or equal to b.

If an inverse block is specified it will be rendered when falsey. You may optionally use the compare="" hash argument for the second value.

Params

  • a {String}

  • b {String}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{has}}

Block helper that renders a block if value has pattern. If an inverse block is specified it will be rendered when falsey.

Params

  • val {any}: The value to check.

  • pattern {any}: The pattern to check for.

  • options {Object}: Handlebars provided options object

  • returns {String}

{{isFalsey}}

Returns true if the given value is falsey. Uses the falsey library for comparisons. Please see that library for more information or to report bugs with this helper.

Params

  • val {any}

  • options {Options}

  • returns {Boolean}

{{isTruthy}}

Returns true if the given value is truthy. Uses the falsey library for comparisons. Please see that library for more information or to report bugs with this helper.

Params

  • val {any}

  • options {Options}

  • returns {Boolean}

{{ifEven}}

Return true if the given value is an even number.

Params

  • number {Number}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

Example

{{ifNth}}

Conditionally renders a block if the remainder is zero when a operand is divided by b. If an inverse block is specified it will be rendered when the remainder is not zero.

Params

  • {}: {Number}

  • {}: {Number}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{ifOdd}}

Block helper that renders a block if value is an odd number. If an inverse block is specified it will be rendered when falsey.

Params

  • value {Object}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

Example

{{is}}

Block helper that renders a block if a is equal to b. If an inverse block is specified it will be rendered when falsey. Similar to eq but does not do strict equality.

Params

  • a {any}

  • b {any}

  • options {Object}: Handlebars provided options object

  • returns {String}

{{isnt}}

Block helper that renders a block if a is not equal to b. If an inverse block is specified it will be rendered when falsey. Similar to unlessEq but does not use strict equality for comparisons.

Params

  • a {String}

  • b {String}

  • options {Object}: Handlebars provided options object

  • returns {String}

{{lt}}

Block helper that renders a block if a is less than b.

If an inverse block is specified it will be rendered when falsey. You may optionally use the compare="" hash argument for the second value.

Params

  • context {Object}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{lte}}

Block helper that renders a block if a is less than or equal to b.

If an inverse block is specified it will be rendered when falsey. You may optionally use the compare="" hash argument for the second value.

Params

  • a {Sring}

  • b {Sring}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{neither}}

Block helper that renders a block if neither of the given values are truthy. If an inverse block is specified it will be rendered when falsey.

Params

  • a {any}

  • b {any}

  • options {}: Handlebars options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{not}}

Returns true if val is falsey. Works as a block or inline helper.

Params

  • val {String}

  • options {Object}: Handlebars provided options object

  • returns {String}

{{or}}

Block helper that renders a block if any of the given values is truthy. If an inverse block is specified it will be rendered when falsey.

Params

  • arguments {...any}: Variable number of arguments

  • options {Object}: Handlebars options object

  • returns {String}: Block, or inverse block if specified and falsey.

Example

{{unlessEq}}

Block helper that always renders the inverse block unless a is equal to b.

Params

  • a {String}

  • b {String}

  • options {Object}: Handlebars provided options object

  • returns {String}: Inverse block by default, or block if falsey.

{{unlessGt}}

Block helper that always renders the inverse block unless a is greater than b.

Params

  • a {Object}: The default value

  • b {Object}: The value to compare

  • options {Object}: Handlebars provided options object

  • returns {String}: Inverse block by default, or block if falsey.

{{unlessLt}}

Block helper that always renders the inverse block unless a is less than b.

Params

  • a {Object}: The default value

  • b {Object}: The value to compare

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{unlessGteq}}

Block helper that always renders the inverse block unless a is greater than or equal to b.

Params

  • a {any}

  • b {any}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

{{unlessLteq}}

Block helper that always renders the inverse block unless a is less than or equal to b.

Params

  • a {any}

  • b {any}

  • options {Object}: Handlebars provided options object

  • returns {String}: Block, or inverse block if specified and falsey.

String helpers

{{append}}

Append the specified suffix to the given string.

Params

  • str {String}

  • suffix {String}

  • returns {String}

Example

{{camelcase}}

camelCase the characters in the given string.

Params

  • string {String}: The string to camelcase.

  • returns {String}

Example

{{capitalize}}

Capitalize the first word in a sentence.

Params

  • str {String}

  • returns {String}

Example

{{capitalizeAll}}

Capitalize all words in a string.

Params

  • str {String}

  • returns {String}

Example

{{center}}

Center a string using non-breaking spaces

Params

  • str {String}

  • spaces {String}

  • returns {String}

{{chop}}

Like trim, but removes both extraneous whitespace and non-word characters from the beginning and end of a string.

Params

  • string {String}: The string to chop.

  • returns {String}

Example

{{dashcase}}

dash-case the characters in string. Replaces non-word characters and periods with hyphens.

Params

  • string {String}

  • returns {String}

Example

{{dotcase}}

dot.case the characters in string.

Params

  • string {String}

  • returns {String}

Example

{{downcase}}

Lowercase all of the characters in the given string. Alias for lowercase.

Params

  • string {String}

  • returns {String}

Example

{{ellipsis}}

Truncates a string to the specified length, and appends it with an elipsis, .

Params

  • str {String}

  • length {Number}: The desired length of the returned string.

  • returns {String}: The truncated string.

Example

{{hyphenate}}

Replace spaces in a string with hyphens.

Params

  • str {String}

  • returns {String}

Example

{{isString}}

Return true if value is a string.

Params

  • value {String}

  • returns {Boolean}

Example

{{lowercase}}

Lowercase all characters in the given string.

Params

  • str {String}

  • returns {String}

Example

{{occurrences}}

Return the number of occurrences of substring within the given string.

Params

  • str {String}

  • substring {String}

  • returns {Number}: Number of occurrences

Example

{{pascalcase}}

PascalCase the characters in string.

Params

  • string {String}

  • returns {String}

Example

{{pathcase}}

path/case the characters in string.

Params

  • string {String}

  • returns {String}

Example

{{plusify}}

Replace spaces in the given string with pluses.

Params

  • str {String}: The input string

  • returns {String}: Input string with spaces replaced by plus signs

Example

{{prepend}}

Prepends the given string with the specified prefix.

Params

  • str {String}

  • prefix {String}

  • returns {String}

Example

{{raw}}

Render a block without processing mustache templates inside the block.

Params

  • options {Object}

  • returns {String}

Example

{{remove}}

Remove all occurrences of substring from the given str.

Params

  • str {String}

  • substring {String}

  • returns {String}

Example

{{removeFirst}}

Remove the first occurrence of substring from the given str.

Params

  • str {String}

  • substring {String}

  • returns {String}

Example

{{replace}}

Replace all occurrences of substring a with substring b.

Params

  • str {String}

  • a {String}

  • b {String}

  • returns {String}

Example

{{replaceFirst}}

Replace the first occurrence of substring a with substring b.

Params

  • str {String}

  • a {String}

  • b {String}

  • returns {String}

Example

{{reverse}}

Reverse a string.

Params

  • str {String}

  • returns {String}

Example

{{sentence}}

Sentence case the given string

Params

  • str {String}

  • returns {String}

Example

{{snakecase}}

snake_case the characters in the given string.

Params

  • string {String}

  • returns {String}

Example

{{split}}

Split string by the given character.

Params

  • string {String}: The string to split.

  • returns {String} character: Default is an empty string.

Example

{{startsWith}}

Tests whether a string begins with the given prefix.

Params

  • prefix {String}

  • testString {String}

  • options {String}

  • returns {String}

Example

{{titleize}}

Title case the given string.

Params

  • str {String}

  • returns {String}

Example

{{trim}}

Removes extraneous whitespace from the beginning and end of a string.

Params

  • string {String}: The string to trim.

  • returns {String}

Example

{{trimLeft}}

Removes extraneous whitespace from the beginning of a string.

Params

  • string {String}: The string to trim.

  • returns {String}

Example

{{trimRight}}

Removes extraneous whitespace from the end of a string.

Params

  • string {String}: The string to trim.

  • returns {String}

Example

{{truncate}}

Truncate a string to the specified length. Also see ellipsis.

Params

  • str {String}

  • limit {Number}: The desired length of the returned string.

  • suffix {String}: Optionally supply a string to use as a suffix to denote when the string has been truncated. Otherwise an ellipsis () will be used.

  • returns {String}: The truncated string.

Example

{{truncateWords}}

Truncate a string to have the specified number of words. Also see truncate.

Params

  • str {String}

  • limit {Number}: The desired length of the returned string.

  • suffix {String}: Optionally supply a string to use as a suffix to denote when the string has been truncated.

  • returns {String}: The truncated string.

Example

{{upcase}}

Uppercase all of the characters in the given string. Alias for uppercase.

Params

  • string {String}

  • returns {String}

Example

{{uppercase}}

Uppercase all of the characters in the given string. If used as a block helper it will uppercase the entire block. This helper does not support inverse blocks.

Params

  • str {String}: The string to uppercase

  • options {Object}: Handlebars options object

  • returns {String}

Example

  • array {Array}: The array to iterate over

  • size {Number}: The desired length of each array "group"

  • options {Object}: Handlebars options

  • returns {String}

Last updated

Was this helpful?