Execute web page js from chrome extension content script

Question

I have this js function in my web page html code.

function update() {
    document.getElementById( "textbox ").value = updatetext;
}

When I execute "update()" from chrome console, it works.
But if I execute from chrome extension,

chrome.tabs.executeScript(tab.id, {code: "update();"}, function(result){});

It says update is not defined. But if I replace with "alert('ok')", It works.
Then I execute

eval("update()")

in Chrome extension content script. It also says "update is not defined."

So what can i do to call js function on web page?

Answer 1

Chrome executes content scripts in a sandbox, so you need to inject an inline script to interact with the webpage:

var injectedCode = 'update()';
var script = document.createElement('script');
script.appendChild(document.createTextNode('('+ injectedCode +')();'));
(document.body || document.head || document.documentElement).appendChild(script);