@metamask/detect-provider

@metamask/detect-provider

A tiny utility for detecting the MetaMask Ethereum provider, or any provider injected at window.ethereum.

It has 0 dependencies and works out of the box in any modern browser, for synchronously and asynchronously injected providers.

Usage

Keep in mind that the providers detected by this package may or may not support the Ethereum JavaScript Provider API. Please consult the MetaMask documentation to learn how to use our provider.

Node.js

import detectEthereumProvider from '@metamask/detect-provider'

const provider = await detectEthereumProvider()

if (provider) {

  console.log('Ethereum successfully detected!')

  // From now on, this should always be true:
  // provider === window.ethereum

  // Access the decentralized web!

  // Legacy providers may only have ethereum.sendAsync
  const chainId = await provider.request({
    method: 'eth_chainId'
  })
} else {

  // if the provider is not detected, detectEthereumProvider resolves to null
  console.error('Please install MetaMask!', error)
}

HTML

<script src="https://unpkg.com/@metamask/detect-provider/dist/detect-provider.min.js"></script>
<script type="text/javascript">
  const provider = await detectEthereumProvider()

  if (provider) {
    // handle provider
  } else {
    // handle no provider
  }
</script>

Options

The exported function takes an optional options object. In most cases, you won't need to specify anything, but read on for details.

options.mustBeMetaMask

Whether window.ethereum.isMetaMask === true is required for the returned Promise to resolve.

Default: false

options.timeout

How many milliseconds to wait for asynchronously injected providers.

Default: 3000

Advanced Topics

Synchronous and Asynchronous Injection

Providers can be either synchronously or asynchronously injected:

• Synchronously injected providers will be available by the time website code starts executing.
• Asynchronously injected providers may not become available until later in the page lifecycle.

The MetaMask extension provider is synchronously injected, while the MetaMask mobile provider is asynchronously injected.

To notify sites of asynchronous injection, MetaMask dispatches the ethereum#initialized event on window immediately after the provider has been set as window.ethereum. This package relies on that event to detect asynchronous injection.

Overwriting or Modifying window.ethereum

The detected provider object returned by this package will strictly equal (===) window.ethereum for the entire page lifecycle, unless window.ethereum is overwritten. In general, consumers should never overwrite window.ethereum or attempt to modify the provider object.

If, as a dapp developer, you notice that the provider returned by this package does not strictly equal window.ethereum, something is wrong. This may happen, for example, if the user has multiple wallets installed. After confirming that your code and dependencies are not modifying or overwriting window.ethereum, you should ask the user to ensure that they only have a single provider-injecting wallet enabled at any one time.

Changelog

[1.0.1] - 2020-06-24

Added

• Initial stable release.