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// so you got an iframe (id="myiframe"). In that page you have an element id="theprice" and you want to change its value
// from the parent page do this in your javascript:
var iframevar = document.getElementById('myiframe');
var elmnt = iframevar.contentWindow.document.getElementById("theprice");
elmnt.innerHTML = theNewPrice;
Change iFrame src attribute
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// Get the iframe by id and set new src attribute
document.querySelector("#viewing-frame").src = "path/to/new/src";
You can also use ".viewing-frame" to get the iframe by class or you can get the iframe directly with "iframe"
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