Load external JS from bookmarklet?

2015 Update

Content security policy will prevent this from working in many sites now. For example, the code below won't work on Facebook.

2008 answer

Use a bookmarklet that creates a script tag which includes your external JS.

As a sample:

javascript:(function(){document.body.appendChild(document.createElement('script')).src='** your external file URL here **';})();

If I can add method tested in FF & Chrome (for readibility split to multiple lines):

javascript:var r = new XMLHttpRequest();
           r.open("GET", "https://...my.js", true);
           r.onloadend = function (oEvent) {
               new Function(r.responseText)();
               /* now you can use your code */
           };
           r.send();
           undefined

It is no longer recommended to do this as CSP on most website will make it fail. But if you still want to use it: 2022 example

(() => {
    const main = () => {
        // write your code here
        alert($('body')[0].innerHTML)
    }
    const scriptEle = document.createElement('script')
    scriptEle.onload = main
    scriptEle.src = 'https://cdn.jsdelivr.net/npm/jquery@3.6.1/dist/jquery.min.js'
    document.body.appendChild(scriptEle)
})();

I always prefer to use a popular open source project loadjs

it is cross browser tested and has more functionality/comfort features.

So the code will look like this:

loadjs=function(){function e(e,n){var t,r,i,c=[],o=(e=e.push?e:[e]).length,f=o;for(t=function(e,t){t.length&&c.push(e),--f||n(c)};o--;)r=e[o],(i=s[r])?t(r,i):(u[r]=u[r]||[]).push(t)}function n(e,n){if(e){var t=u[e];if(s[e]=n,t)for(;t.length;)t[0](e,n),t.splice(0,1)}}function t(e,n,r,i){var o,s,u=document,f=r.async,a=(r.numRetries||0)+1,h=r.before||c;i=i||0,/(^css!|\.css$)/.test(e)?(o=!0,(s=u.createElement("link")).rel="stylesheet",s.href=e.replace(/^css!/,"")):((s=u.createElement("script")).src=e,s.async=void 0===f||f),s.onload=s.onerror=s.onbeforeload=function(c){var u=c.type[0];if(o&&"hideFocus"in s)try{s.sheet.cssText.length||(u="e")}catch(e){u="e"}if("e"==u&&(i+=1)<a)return t(e,n,r,i);n(e,u,c.defaultPrevented)},!1!==h(e,s)&&u.head.appendChild(s)}function r(e,n,r){var i,c,o=(e=e.push?e:[e]).length,s=o,u=[];for(i=function(e,t,r){if("e"==t&&u.push(e),"b"==t){if(!r)return;u.push(e)}--o||n(u)},c=0;c<s;c++)t(e[c],i,r)}function i(e,t,i){var s,u;if(t&&t.trim&&(s=t),u=(s?i:t)||{},s){if(s in o)throw"LoadJS";o[s]=!0}r(e,function(e){e.length?(u.error||c)(e):(u.success||c)(),n(s,e)},u)}var c=function(){},o={},s={},u={};return i.ready=function(n,t){return e(n,function(e){e.length?(t.error||c)(e):(t.success||c)()}),i},i.done=function(e){n(e,[])},i.reset=function(){o={},s={},u={}},i.isDefined=function(e){return e in o},i}();
loadjs('//path/external/js', {
    success: function () {
        console.log('something to run after the script was loaded');
    });