addInitScript

Adds a script which would be evaluated in one of the following scenarios:

• Whenever the page is navigated.
• Whenever the child frame is attached or navigated. In this case, the script is evaluated in the context of the newly attached frame.

The script is evaluated after the document was created but before any of its scripts were run. In order to remove the initialization script from the page again, call the function that got returned by this function.

This is useful to amend the JavaScript environment, e.g. to seed Math.random.

Usage

browser.addInitScript(script, args)

Parameters

Name	Type	Details
script	Function	function to be injected as initialization script
args	number, string, boolean	parameters for the script

Examples

addInitScript.js

const script = await browser.addInitScript((seed) => {
    Math.random = () => seed
}, 42)

await browser.url('https://webdriver.io')
console.log(await browser.execute(() => Math.random())) // returns 42

await reset()
await browser.url('https://webdriver.io')
console.log(await browser.execute(() => Math.random())) // returns a random number

hermore you can also use the `emit` function to send data back to the Node.js environment.
 is useful if you want to observe certain events in the browser environment, e.g.:

addInitScriptWithEmit.js

const script = await browser.addInitScript((emit) => {
  const observer = new MutationObserver((mutations) => {
    for (const mutation of mutations) {
      emit(mutation.target.nodeName)
    }
  })
  observer.observe(document, { childList: true, subtree: true })
})

script.on('data', (data) => {
  console.log(data) // prints: BODY, DIV, P, ...
})