Node.js v7 has updated V8 to 5.4

Michaël Zasso

With the release of Node.js 7.0.0, the V8 JavaScript engine has been upgraded from 5.1 to its latest stable version, 5.4. It brings in new language features and increased performance.

New ECMAScript features

Exponentiation operator (ES2016)

• Proposal
• Spec

The ** operator can now be used to raise the left-hand side to the power of the right-hand side. Example:

const maxInt = 2 ** 32 - 1; // Equivalent to: Math.pow(2, 32) - 1

Object.values / Object.entries (ES2017)

• Proposal
• Spec (draft)

Complementing Object.keys, those two new static methods return respectively an Array of enumerable own property values or entries (an entry being an array with two elements: key and value). Example:

const obj = {
  x: 0,
  y: 100,
};

const keys = Object.keys(obj); // ['x', 'y']
const values = Object.values(obj); // [0, 100]
const entries = Object.entries(obj); // [['x', 0], ['y', 100]]

Object.getOwnPropertyDescriptors (ES2017)

• Proposal
• Spec (draft)

Returns all own property descriptors of an Object in a new Object, mapped by their respective key. Example:

const obj = {
  x: 0,
  y: 100,
};

const descriptors = Object.getOwnPropertyDescriptors(obj);
/*
{ x: {value: 0, writable: true, enumerable: true, configurable: true},
  y: {value: 100, writable: true, enumerable: true, configurable: true} }
*/

Performance and memory optimizations

From V8 5.2

Improvement of JavaScript built-ins, including:

• Array operations like the isArray method.
• The in operator.
• Function.prototype.bind.

From V8 5.3

• The new Ignition interpreter is now feature complete and can be tested with the flag --ignition. Read the blog post from V8's team for more information.
• The garbage collector has been improved and full garbage collection pause times can be reduced up to 25%.
• Improvement of ES6 Promise performance.

From V8 5.4

• Reduced on-heap peak memory consumption on low-memory devices up to 40%.
• Optimizations in V8's parser allowed to reduce off-heap peak memory consumption up to 20% and improve startup performance.