Passing Parameters to Content Scripts Injected with chrome.tabs.executeScript()

When injecting a content script file using chrome.tabs.executeScript({file: "content.js"}), a common question arises: how to pass parameters to the JavaScript within the content script file?

Parameter Passing Fallacy

It's important to clarify that you cannot directly pass parameters to a file. Instead, you have two options for achieving this functionality:

1. Setting Parameters Before File Execution

Nest chrome.tabs.executeScript calls to define variables before injecting the file:

chrome.tabs.executeScript(tab.id, {
    code: 'var config = 1;'
}, function() {
    chrome.tabs.executeScript(tab.id, {file: 'content.js'});
});

For complex variables, consider using JSON.stringify to convert an object into a string:

var config = {somebigobject: 'complicated value'};
chrome.tabs.executeScript(tab.id, {
    code: 'var config = '   JSON.stringify(config)
}, function() {
    chrome.tabs.executeScript(tab.id, {file: 'content.js'});
});

In content.js, you can access these variables:

// content.js
alert('Example:'   config);

2. Setting Parameters After File Execution

Execute the file first, then use the message passing API to send parameters:

chrome.tabs.executeScript(tab.id, {file: 'content.js'}, function() {
    chrome.tabs.sendMessage(tab.id, 'whatever value; String, object, whatever');
});

In content.js, listen for these messages using chrome.runtime.onMessage and handle the message:

chrome.runtime.onMessage.addListener(function(message, sender, sendResponse) {
    // Handle message.
    // In this example, message === 'whatever value; String, object, whatever'
});