ES Feature List

These two tables are taken from @kangax's great browser compatibility matrices, with the wiki conversion losing a lot of nice formatting, alas.

ES5	EJS Support	ES6	EJS Support
Object.create	Yes	computed properties	No
Object.defineProperty	Yes	arrow functions	Yes
Object.defineProperties	Yes	class	Yes
Object.getPrototypeOf	Yes	let	Yes
Object.keys	No	const	No
Object.seal	Yes	default function params	Yes[2]
Object.freeze	Yes	rest parameters	Yes
Object.preventExtensions	Yes	spread call (...) operator	No
Object.isSealed	Yes	spread array (...) operator	No
Object.isExtensible	Yes	Modules	No
Object.getOwnPropertyDescriptor	Yes	For..of loops	No
Object.getOwnPropertyNames	Yes	Array comprehensions	No
Date.prototype.toISOString	No	Generator comprehensions	No
Date.now	Yes	Iterators	No
Array.isArray	Yes	Generators (yield)	No
JSON	Yes	Template Strings	No
Function.prototype.bind	Yes	RegExp "y" flag	No
String.prototype.trim	No	Map	Partial
Array.prototype.indexOf	Yes	Set	No
Array.prototype.lastIndexOf	Yes	WeakMap	No
Array.prototype.every	Yes	WeakSet	No
Array.prototype.some	Yes	Proxy	No
Array.prototype.forEach	Yes	Struct (binary data storage)	No
Array.prototype.map	Yes	Block-level function declaration	Yes
Array.prototype.filter	No	Destructuring	Yes
Array.prototype.reduce	Yes	Promise	No
Array.prototype.reduceRight	Yes	Object.assign	No
Getter in property initializer	No	Object.getOwnPropertyDescriptors	No
Setter in property initializer	No	Object.getPropertyDescriptor	No
Property access on strings	Yes	Object.getPropertyNames	No
Reserved words as property names	Yes	Object.is	No
Zero-width chars in identifiers		Object.setPrototypeOf	No
Immutable undefined	No	Object.observe (part of ES7)	No
Strict mode	Yes	String.fromCodePoint	No
new Function	No [1]	String.prototype.codePointAt	No
eval	No [1]	String.prototype.repeat	No

                             |                        | String.prototype.startsWith      | **No**
                             |                        | String.prototype.endWith         | **No**
                             |                        | String.prototype.contains        | **No**
                             |                        | String.prototype.toArray         | **No**
                             |                        | Symbol                           | **No**
                             |                        | Unicode code point escapes       | **No**
                             |                        | Array.from                       | Yes
                             |                        | Array.of                         | Yes
                             |                        | Array.prototype.find             | Yes
                             |                        | Array.prototype.findIndex        | Yes
                             |                        | Array.prototype.fill             | **No**
                             |                        | Number.isFinite                  | **No**
                             |                        | Number.isInteger                 | **No**
                             |                        | Number.isNaN                     | **No**
                             |                        | Number.toInteger                 | **No**
                             |                        | Number.prototype.clz             | **No**
                             |                        | Math.imul                        | **No**
                             |                        | Math.sign                        | **No**
                             |                        | Math.log10                       | **No**
                             |                        | Math.log2                        | **No**
                             |                        | Math.log1p                       | **No**
                             |                        | Math.expm1                       | **No**
                             |                        | Math.cosh                        | **No**
                             |                        | Math.sinh                        | **No**
                             |                        | Math.tanh                        | **No**
                             |                        | Math.acosh                       | **No**
                             |                        | Math.asinh                       | **No**
                             |                        | Math.atanh                       | **No**
                             |                        | Math.hypot                       | **No**
                             |                        | Math.trunc                       | **No**
                             |                        | Math.fround                      | **No**

Notes:

1. as a static compiler, ejs doesn't support these constructs as they generally require runtime code generation.
2. ejs incorrectly uses the default parameter value if undefined is passed for that argument.