JavaScript runtime 1.0 features for CloudFront Functions - Amazon CloudFront
Core featuresPrimitive objectsBuilt-in objectsError typesGlobalsBuilt-in modulesRestricted features
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JavaScript runtime 1.0 features for CloudFront Functions

The CloudFront Functions JavaScript runtime environment is compliant with ECMAScript (ES) version 5.1 and also supports some features of ES versions 6 through 9. It also provides some nonstandard methods that are not part of the ES specifications.

The following topics list all the supported language features.

Core features

The following core features of ES are supported.

Types

All ES 5.1 types are supported. This includes Boolean values, numbers, strings, objects, arrays, functions, function constructors, and regular expressions.

Operators

All ES 5.1 operators are supported.

The ES 7 exponentiation operator (**) is supported.

Statements
Note

The const and let statements are not supported.

The following ES 5.1 statements are supported:

  • break

  • catch

  • continue

  • do-while

  • else

  • finally

  • for

  • for-in

  • if

  • return

  • switch

  • throw

  • try

  • var

  • while

  • Labeled statements

Literals

ES 6 template literals are supported: multiline strings, expression interpolation, and nesting templates.

Functions

All ES 5.1 function features are supported.

ES 6 arrow functions are supported, and ES 6 rest parameter syntax is supported.

Unicode

Source text and string literals can contain Unicode-encoded characters. Unicode code point escape sequences of six characters (for example, \uXXXX) are also supported.

Strict mode

Functions operate in strict mode by default, so you don’t need to add a use strict statement in your function code. This cannot be changed.

Primitive objects

The following primitive objects of ES are supported.

Object

The following ES 5.1 methods on objects are supported:

  • create (without properties list)

  • defineProperties

  • defineProperty

  • freeze

  • getOwnPropertyDescriptor

  • getOwnPropertyNames

  • getPrototypeOf

  • hasOwnProperty

  • isExtensible

  • isFrozen

  • prototype.isPrototypeOf

  • isSealed

  • keys

  • preventExtensions

  • prototype.propertyIsEnumerable

  • seal

  • prototype.toString

  • prototype.valueOf

The following ES 6 methods on objects are supported:

  • assign

  • is

  • prototype.setPrototypeOf

The following ES 8 methods on objects are supported:

  • entries

  • values

String

The following ES 5.1 methods on strings are supported:

  • fromCharCode

  • prototype.charAt

  • prototype.concat

  • prototype.indexOf

  • prototype.lastIndexOf

  • prototype.match

  • prototype.replace

  • prototype.search

  • prototype.slice

  • prototype.split

  • prototype.substr

  • prototype.substring

  • prototype.toLowerCase

  • prototype.trim

  • prototype.toUpperCase

The following ES 6 methods on strings are supported:

  • fromCodePoint

  • prototype.codePointAt

  • prototype.endsWith

  • prototype.includes

  • prototype.repeat

  • prototype.startsWith

The following ES 8 methods on strings are supported:

  • prototype.padStart

  • prototype.padEnd

The following ES 9 methods on strings are supported:

  • prototype.trimStart

  • prototype.trimEnd

The following nonstandard methods on strings are supported:

  • prototype.bytesFrom(array | string, encoding)

    Creates a byte string from an array of octets or an encoded string. The string encoding options are hex, base64, and base64url.

  • prototype.fromBytes(start[, end])

    Creates a Unicode string from a byte string where each byte is replaced with the corresponding Unicode code point.

  • prototype.fromUTF8(start[, end])

    Creates a Unicode string from a UTF-8 encoded byte string. If the encoding is incorrect, it returns null.

  • prototype.toBytes(start[, end])

    Creates a byte string from a Unicode string. All characters must be in the [0,255] range. If not, it returns null.

  • prototype.toUTF8(start[, end])

    Creates a UTF-8 encoded byte string from a Unicode string.

Number

All ES 5.1 methods on numbers are supported.

The following ES 6 methods on numbers are supported:

  • isFinite

  • isInteger

  • isNaN

  • isSafeInteger

  • parseFloat

  • parseInt

  • prototype.toExponential

  • prototype.toFixed

  • prototype.toPrecision

  • EPSILON

  • MAX_SAFE_INTEGER

  • MAX_VALUE

  • MIN_SAFE_INTEGER

  • MIN_VALUE

  • NEGATIVE_INFINITY

  • NaN

  • POSITIVE_INFINITY

Built-in objects

The following built-in objects of ES are supported.

Math

All ES 5.1 math methods are supported.

Note

In the CloudFront Functions runtime environment, the Math.random() implementation uses OpenBSD arc4random seeded with the timestamp of when the function runs.

The following ES 6 math methods are supported:

  • acosh

  • asinh

  • atanh

  • cbrt

  • clz32

  • cosh

  • expm1

  • fround

  • hypot

  • imul

  • log10

  • log1p

  • log2

  • sign

  • sinh

  • tanh

  • trunc

  • E

  • LN10

  • LN2

  • LOG10E

  • LOG2E

  • PI

  • SQRT1_2

  • SQRT2

Date

All ES 5.1 Date features are supported.

Note

For security reasons, Date always returns the same value—the function’s start time—during the lifetime of a single function run. For more information, see Restricted features.

Function

The apply, bind, and call methods are supported.

Function constructors are not supported.

Regular expressions

All ES 5.1 regular expression features are supported. The regular expression language is Perl compatible. ES 9 named capture groups are supported.

JSON

All ES 5.1 JSON features are supported, including parse and stringify.

Array

The following ES 5.1 methods on arrays are supported:

  • isArray

  • prototype.concat

  • prototype.every

  • prototype.filter

  • prototype.forEach

  • prototype.indexOf

  • prototype.join

  • prototype.lastIndexOf

  • prototype.map

  • prototype.pop

  • prototype.push

  • prototype.reduce

  • prototype.reduceRight

  • prototype.reverse

  • prototype.shift

  • prototype.slice

  • prototype.some

  • prototype.sort

  • prototype.splice

  • prototype.unshift

The following ES 6 methods on arrays are supported:

  • of

  • prototype.copyWithin

  • prototype.fill

  • prototype.find

  • prototype.findIndex

The following ES 7 methods on arrays are supported:

  • prototype.includes

Typed arrays

The following ES 6 typed arrays are supported:

  • Int8Array

  • Uint8Array

  • Uint8ClampedArray

  • Int16Array

  • Uint16Array

  • Int32Array

  • Uint32Array

  • Float32Array

  • Float64Array

  • prototype.copyWithin

  • prototype.fill

  • prototype.join

  • prototype.set

  • prototype.slice

  • prototype.subarray

  • prototype.toString

ArrayBuffer

The following methods on ArrayBuffer are supported:

  • prototype.isView

  • prototype.slice

Promise

The following methods on promises are supported:

  • reject

  • resolve

  • prototype.catch

  • prototype.finally

  • prototype.then

Crypto

The cryptographic module provides standard hashing and hash-based message authentication code (HMAC) helpers. You can load the module using require('crypto'). The module exposes the following methods that behave exactly as their Node.js counterparts:

  • createHash(algorithm)

  • hash.update(data)

  • hash.digest([encoding])

  • createHmac(algorithm, secret key)

  • hmac.update(data)

  • hmac.digest([encoding])

For more information, see Crypto (hash and HMAC) in the built-in modules section.

Console

This is a helper object for debugging. It only supports the log() method, to record log messages.

Note

CloudFront Functions doesn't support comma syntax, such as console.log('a', 'b'). Instead, use the console.log('a' + ' ' + 'b') format.

Error types

The following error objects are supported:

  • Error

  • EvalError

  • InternalError

  • MemoryError

  • RangeError

  • ReferenceError

  • SyntaxError

  • TypeError

  • URIError

Globals

The globalThis object is supported.

The following ES 5.1 global functions are supported:

  • decodeURI

  • decodeURIComponent

  • encodeURI

  • encodeURIComponent

  • isFinite

  • isNaN

  • parseFloat

  • parseInt

The following global constants are supported:

  • NaN

  • Infinity

  • undefined

Built-in modules

The following built-in modules are supported.

Crypto (hash and HMAC)

The cryptographic module (crypto) provides standard hashing and hash-based message authentication code (HMAC) helpers. You can load the module using require('crypto'). The module provides the following methods that behave exactly as their Node.js counterparts.

Hashing methods

crypto.createHash(algorithm)

Creates and returns a hash object that you can use to generate hash digests using the given algorithm: md5, sha1, or sha256.

hash.update(data)

Updates the hash content with the given data.

hash.digest([encoding])

Calculates the digest of all of the data passed using hash.update(). The encoding can be hex, base64, or base64url.

HMAC methods

crypto.createHmac(algorithm, secret key)

Creates and returns an HMAC object that uses the given algorithm and secret key. The algorithm can be md5, sha1, or sha256.

hmac.update(data)

Updates the HMAC content with the given data.

hmac.digest([encoding])

Calculates the digest of all of the data passed using hmac.update(). The encoding can be hex, base64, or base64url.

Query string

Note

The CloudFront Functions event object automatically parses URL query strings for you. That means that in most cases you don’t need to use this module.

The query string module (querystring) provides methods for parsing and formatting URL query strings. You can load the module using require('querystring'). The module provides the following methods.

querystring.escape(string)

URL-encodes the given string, returning an escaped query string. The method is used by querystring.stringify() and should not be used directly.

querystring.parse(string[, separator[, equal[, options]]])

Parses a query string (string) and returns an object.

The separator parameter is a substring for delimiting key and value pairs in the query string. By default it is &.

The equal parameter is a substring for delimiting keys and values in the query string. By default it is =.

The options parameter is an object with the following keys:

decodeURIComponent function

A function to decode percent-encoded characters in the query string. By default it is querystring.unescape().

maxKeys number

The maximum number of keys to parse. By default it is 1000. Use a value of 0 to remove the limitations for counting keys.

By default, percent-encoded characters within the query string are assumed to use the UTF-8 encoding. Invalid UTF-8 sequences are replaced with the U+FFFD replacement character.

For example, for the following query string:

'name=value&abc=xyz&abc=123'

The return value of querystring.parse() is:

{
name: 'value',
abc: ['xyz', '123']
}

querystring.decode() is an alias for querystring.parse().

querystring.stringify(object[, separator[, equal[, options]]])

Serializes an object and returns a query string.

The separator parameter is a substring for delimiting key and value pairs in the query string. By default it is &.

The equal parameter is a substring for delimiting keys and values in the query string. By default it is =.

The options parameter is an object with the following keys:

encodeURIComponent function

The function to use for converting URL-unsafe characters to percent-encoding in the query string. By default it is querystring.escape().

By default, characters that require percent-encoding within the query string are encoded as UTF-8. To use a different encoding, specify the encodeURIComponent option.

For example, for the following code:

querystring.stringify({ name: 'value', abc: ['xyz', '123'], anotherName: '' });

The return value is:

'name=value&abc=xyz&abc=123&anotherName='

querystring.encode() is an alias for querystring.stringify().

querystring.unescape(string)

Decodes URL percent-encoded characters in the given string, returning an unescaped query string. This method is used by querystring.parse() and should not be used directly.

Restricted features

The following JavaScript language features are either unsupported or restricted due to security concerns.

Dynamic code evaluation

Dynamic code evaluation is not supported. Both eval() and Function constructors throw an error if attempted. For example, const sum = new Function('a', 'b', 'return a + b') throws an error.

Timers

The setTimeout(), setImmediate(), and clearTimeout() functions are not supported. There is no provision to defer or yield within a function run. Your function must synchronously run to completion.

Date and timestamps

For security reasons, there is no access to high-resolution timers. All Date methods to query the current time always return the same value during the lifetime of a single function run. The returned timestamp is the time when the function started running. Consequently, you cannot measure elapsed time in your function.

File system access

There is no file system access. For example, there is no fs module for file system access like there is in Node.js.

Network access

There is no support for network calls. For example, XHR, HTTP(S), and socket are not supported.