How to change all texts in DOM without breaking existing HTML?

Question

I want to replace specific texts on a page with javascript. For simplicty lets say I want to replace all letters A with the letter X. Important is that it's not going to break inline HTML.

Is there a simple way to iterate over all DOM elements and only change actual texts?

<span>hello world <a href="/">abcd</a>..</span>

should become

<span>hello world <a href="/">xbcd</a>..</span>

and not

<spxn>hello world <x href="/">xbcd</x>..</spxn>

Assign all the spans the same class id then use JQuery to change the text of all elements with that class name. — SPlatten, Sep 06 '19 at 10:57
Possible duplicate of [Javascript .replace command replace page text?](https://stackoverflow.com/questions/7275650/javascript-replace-command-replace-page-text) — wOxxOm, Sep 06 '19 at 11:01

CertainPerformance · Accepted Answer · 2019-09-06T11:19:12.537

Iterate over all text nodes, and change their nodeValue if they contain an a:

function getAllTextNodes() {
    var walker = document.createTreeWalker(
        document.body, 
        NodeFilter.SHOW_TEXT, 
        null, 
        false
    );

    var node;
    var textNodes = [];

    while(node = walker.nextNode()) {
        textNodes.push(node);
    }
    return textNodes;
}

getAllTextNodes().forEach((node) => {
  const { nodeValue } = node;
  const newValue = nodeValue.replace(/a/g, 'x');
  if (newValue !== nodeValue) {
    node.nodeValue = newValue;
  }
});

<a href="/">abcd</a>

You can also create a whitelist or blacklist of parents whose text nodes are changeable, if you want:

function getAllTextNodes() {
    var walker = document.createTreeWalker(
        document.body, 
        NodeFilter.SHOW_TEXT, 
        null, 
        false
    );

    var node;
    var textNodes = [];

    while(node = walker.nextNode()) {
        textNodes.push(node);
    }
    return textNodes;
}

const tagNamesToKeepUnchanged = ['SCRIPT'];

getAllTextNodes().forEach((node) => {
  if (tagNamesToKeepUnchanged.includes(node.parentNode.tagName)) {
    return;
  }
  const { nodeValue } = node;
  const newValue = nodeValue.replace(/a/g, 'x');
  if (newValue !== nodeValue) {
    node.nodeValue = newValue;
  }
});

const obj = JSON.parse(
  document.querySelector('script[type="application/json"]').textContent
);
console.log(obj.key);

<a href="/">abcd</a>
<p>foo bar</p>
<script type="application/json">{"key":"value"}</script>

This will preserve tag names, event listeners, and pretty much everything except the content of certain text nodes.

Oh, that's true, though luckily it probably doesn't matter since the scripts will have already been executed. You can make a whitelist of parent elements whose text is changeable (or a blacklist) if you want — CertainPerformance, Sep 06 '19 at 11:03
It doesn't matter because scripts runs just once when they were added, and it's really trivial to check if for some reason someone wants that. — wOxxOm, Sep 06 '19 at 11:03
This is cool answer, I didn't know about `createTreeWalker`! +1 — Tomáš Zato - Reinstate Monica, Sep 06 '19 at 11:11
it actually matters. it manipulates functions within script blocks which gets me exceptions later on. — boop, Sep 06 '19 at 11:13

Tomáš Zato - Reinstate Monica · Answer 2 · 2019-09-06T11:11:55.620

I usually use this:

/**
 * Executes operation over all text nodes in a document
 * @param {HTMLElement} element
 * @param {function(Text):void} callback
 */
function processTextNodes(element, callback) {
    // For text node, execute callback
    if (element.nodeType == Node.TEXT_NODE)
        callback(element);
    // Otherwise, loop over child nodes
    else if (element.childNodes.length > 0) {
        for (const childNode of element.childNodes) {
            if (childNode.nodeType == Node.TEXT_NODE)
                callback(childNode);
            // Recursion to child nodes
            else {
                processTextNodes(childNode, callback);
            }
        }
    }
}

For example try this:

processTextNodes(document.body, (el)=>{el.data = el.data.toUpperCase()})

I used this in several userscripts that replace words in news articles to make them more fun.

How to change all texts in DOM without breaking existing HTML?

2 Answers2