Javascript .replace command replace page text?

The .replace method is a string operation, so it’s not immediately simple to run the operation on HTML documents, which are composed of DOM Node objects.

Use TreeWalker API

The best way to go through every node in a DOM and replace text in it is to use the document.createTreeWalker method to create a TreeWalker object. This is a practice that is used in a number of Chrome extensions!

// create a TreeWalker of all text nodes
var allTextNodes = document.createTreeWalker(document.body, NodeFilter.SHOW_TEXT),
    // some temp references for performance
    tmptxt,
    tmpnode,
    // compile the RE and cache the replace string, for performance
    cakeRE = /cake/g,
    replaceValue = "pie";

// iterate through all text nodes
while (allTextNodes.nextNode()) {
    tmpnode = allTextNodes.currentNode;
    tmptxt = tmpnode.nodeValue;
    tmpnode.nodeValue = tmptxt.replace(cakeRE, replaceValue);
}

To replace parts of text with another element or to add an element in the middle of text, use DOM splitText, createElement, and insertBefore methods, example.

See also how to replace multiple strings with multiple other strings.

Don’t use innerHTML or innerText or jQuery .html()

// the innerHTML property of any DOM node is a string
document.body.innerHTML = document.body.innerHTML.replace(/cake/g,'pie')

• It’s generally slower (especially on mobile devices).
• It effectively removes and replaces the entire DOM, which is not awesome and could have some side effects: it destroys all event listeners attached in JavaScript code (via addEventListener or .onxxxx properties) thus breaking the functionality partially/completely.
• This is, however, a common, quick, and very dirty way to do it.